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Black Holes Most scientists agree that black holes exist but are nearly impossible to locate. A．black hole in the universe is not a solid object, like a planet, but it is shaped like a sphere (球体). Astronomers (天文学家) think that at the center of a black hole there is a single point in space with infinite (无限的) density (稠密). This single point is called a singularity (奇点). If the singularity theory is correct, it means that when a massive star collapses, all the material in it disappears into the singularity. The center of a black hole would not really be a hole at all, but an infinitely dense point. Anything that crosses the black hole is pulled in by its great gravity. Although black holes do exist, they are difficult to observe. These are the reasons. ·No light or anything else comes out of black holes. As a result, they are invisible to a telescope. ·In astronomical terms, black holes are truly tiny. For example, a black hole formed by the collapse of a giant star would have an event horizon (视界) only 18 miles across. ·The nearest black holes would be dozens of light years away from Earth. One light year is about 6 trillion (万亿) miles. Even the most powerful telescopes could not pick out an object so small at such a great distance. In 1994 the Hubble Space Telescope provided evidence that black holes exist. There are still answers to be found, however, so black holes remain one of the mysteries of the universe. Black holes exist but are difficult to observe.
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New Product Will Save lives Drinking water that looks clean may still contain bugs (虫子), which can cause illness. A small company called Genera Technologies has produced a testing method in three stages, which shows whether water is safe. The new test shows if water needs chemicals added to it, to destroy anything harmful. It was invented by scientist Dr. Adrian Parton, who started Genera five years ago. He and his employees have developed the test together with a British water company. Andy Headland, Genera’s marketing director, recently presented the test at a conference in the USA and forecast good American sales for it. Genera has already sold 11 of its tests at $42,500 a time in the UK and has a further four on order. It expects to sell another 25 tests before the end of March. The company says it is the only test in the UK to be approved by the government. Genera was formed five years ago and until October last year had only five employees; it now employs 14. Mr Headland believes that the company should make around $19 million by the end of the year in the UK alone. Genera Technologies orders 25 more tests before the end of the year.
Earthquake How does an earthquake start What makes an earthquake happen The rock of the earth’s crust (地壳) may have a "fault", a kind of break in the surface. The blocks which make up the earth move, and sometimes this may cause the sides of the fault to move up and down or lengthways (纵向) against each other. When one piece of rock starts to rub on another with great force, a lot of energy is used. This energy is changed into vibrations (振动) and it is these vibrations that we feel as an earthquake. The vibrations can travel thousands of kilometers and so an earthquake in Turkey may be felt in Greece, What to do during an earthquake At school As soon as the earthquake starts, students should get under the desks immediately and wait until the teacher tells them it is safe to come out. The teacher should, at the same time, go immediately to the teacher’s desk, get underneath (在……下面) it and stay there till the danger is over. Students must not argue with the teacher or question instructions. As soon as the tremors (震动) stop, all students should walk towards the exit and go straight to the school playground or any open space such as a square or a park. They must wait there until the teacher tells them it is safe to go. At home If you are at home when the earthquake occurs, get immediately under the table in the living room or kitchen. Choose the biggest and strongest table you can find. You must not go anywhere near the window and don’t go out onto the balcony (阳台). Once the tremors have stopped, you can come out from under the table but you must leave the building straight away. You should walk down the stairs and should not use the lift—there may be a power cut as a result of the earthquake and you could find yourself trapped inside the lift for hours. In the street If you are in the street when the earthquake takes place, do not stand near buildings, fences or walls—move away as quickly as possible and try to find a large open space to wait in. Standing under trees could also be dangerous. As soon as an earthquake occurs, students should leave the building.
Seed Dispersal A. They fly, float, hitchhike—and even explode. But the many clever ways seeds get around make sense: after all, a plant’s life depends on finding fertile ground in which to grow. The quest for survival has even led plants to develop delightful and devious ways of fooling us into working for them as they send their seeds out to conquer new lands. Birds help some fruits like the like the cherry by eating the fruit around the seed. The mistletoe’s seeds are covered with a sticky substance that substance that sticks to the bird that tries to eat it. The mistletoe’s seeds have to land on the or they die. Some seeds travel by sailing in the wind. Others hitchhike on animals. Some just get blown in the wind. Seeds can also grow in a flower and drop to the ground. When the seed leaves the flower of whatever it was in, it’s called dissemination. This is one of the most important steps in the seed’s life. Some tree seeds drop directly below the parent and die because there is not enough light or food for them to grow. B. The seeds that travel by wind must be light-weight. Some of these seeds have wings, like the maple seed. Some of these seeds have gone 32 miles on a windy day. Another flying seed is the dandelion which gets planted because ants carry the seeds down into their hole. C. Many plants use wind or water to carry their seeds, which are attached to fine, fluffy fibers that act as parachutes. Milkweed and thistle are among the plants whose seeds fly through the air. Trees such as willow, cottonwood, and sycamore, which grow along streams or creeks, drop many of their seeds into the water, where the fluff keeps them afloat on the current so it can carry them to new spots. Coconuts may drift for several months and travel for up to 1,200 miles (2,000 kin) before reaching dry land. The coconuts are able to float because of special fibers around their seeds. D. The hitchhikers are built with spikes, such as: the squirting cucumber. Then they travel to another place to grow. Some plants have sacks that explode, bursts open and shoot its seeds up to 27 feet (8m) away from the parent plant. The seeds zoom off and may travel as fast as 62 miles (100kin) per hour. Then there are the leapers, seeds that bounce or jump away from the parent plant. Jewelweed and witch hazel have seed cases that are so constructed that when they dry out, the slightest touch causes the case to burst and project the mature seeds through the air. Black walnuts have spongy hulls so that they bounce when they hit the ground and roll away from the tree. E. At first glance some seeds’ designs make plants seem downright intelligent. Take apples, for instance. These sweet fruits have evolved to be bright and shiny for good reason: they attract people and other animals. Drawn in by their effective advertising, we do the work of carrying apple seeds to new territory where the species can gain a toehold and expand. Indeed, we like apples so much that we’ve planted orchards especially for our favorite fruit. The practice has prompted some biologists to ask who really is the boss in this relationship, do the apple trees work for us—or do we work for them F. Similar examples can be found throughout nature, from fig-eating bats that become unwitting cargo planes for fig seeds, to squirrels and woodpeckers that unknowingly help oak trees spread their acorns. An African melon that grows a gourd-shaped bladder of water deep underground. In the dry season, aardvarks sniff out the watery melons, digging deep to quench their thirst. In the process, however, the thirsty aardvarks also sip up a few pit-like seeds, which they later deposit inside fertilizing manure. It’s hard to say who gets the better end of the deal: the melon or the mammal. G. Both plant and animal, of course, get something out of these mutually beneficial relationships. Apple trees, for instance, didn’t set out to fool people into picking their fruit. But somewhere along the line, certain apple trees ended up with a combination of genes that made their fruit a bit brighter or sweeter than all the other apples. Since we liked these apples so much, we began selectively planting the trees, and learned how to breed even sweeter varieties. In exchange for the tender, nutritious fruit, the trees get steady care and even protection from potential enemies, such as insects and browsing deer. H. Evolutionary accidents may explain how other types of seeds developed, too. On the island of Mauritius, for instance, there once were trees that dropped their tasty fruits full of seeds to the ground. Then, a new bird arrived on the island. It loved the fruits, but the tree’s seeds couldn’t survive the trip through the bird’s stomach. As a result, the tree was in trouble, since fewer of its seeds were surviving. Then, perhaps through a random genetic mutation, one tree, produced fruit with tougher seeds that could survive being eaten by the birds. Given this significant advantage, the tougher calvaria soon began to thrive. Eventually, they crowded out their ancestors completely. I. However evolution can sometimes produce a plant that is too reliant on a particular animal for survival. That’s exactly what happened on Mauritius. There, some biologists believe that lonely 300-year-old calvaria trees await a bird that will never return: the dodo. In 1598, Dutch explorers established a colony on Mauritius. In the search for food to eat and sell, the settlers plundered the island’s natural resources, killing giant turtles, lizards, and the huge, flightless dodo birds with abandon. When the settlers did in the dodo, however, they may have also put the death of the calvaria in motion. Some biologists believe the dodos ate the tree’s fruit, and that the trip through the bird’s stomach helped prepare the seeds for germination. But now that their partner in life is gone, only a few calvaria survive. They are silent reminders of a lost past, with their seed-bearing fruit littering the ground and inviting a feast that will never come. Calvaria trees on Mauritins depend on some bird to help their seeds sprout.
Humanity’s greatest accomplishment of the past five decades, declared Bill Gates this week, is the reduction in the number of deaths among young children by half, to 10 million a year in 2007. The world’s most successful capitalist heaped praise on the World Health Organization (WHO), while unveiling an ambitious new global scheme to eliminate polio within a few years. For his part, the agency’s top polio man, Brace Aylward, described the fight against the disease in the language of markets: "Elimination is the venture capital of public health: the risks are huge but so too are the rewards." The use of this sort of language captures a change in public health in the past decade. The Gates Foundation, with its pots of money and businesslike approach, has transformed the bureaucratic and disheartened world of public health. It has helped revive ailing campaigns, including the fight against polio. This will now get a fresh $600m—plus, from British and German taxpayers, from the Rotary Club International, as well as from the Gates Foundation ($255m). The decline from 350,000 new cases in 1988 (when the goal of rapid polio eradication was first declared) to 2,000 cases now (chiefly in Nigeria, India, Pakistan and Afghanistan) looks like a near victory. But the final stretch is the hardest. Only one in 200 cases is readily vulnerable to early detection (as opposed to most victims of smallpox—a serious infectious disease that causes spots which leave deep marks on the skin, already eliminated). Polio is also far more infectious. Other obstacles are that the usual vaccine has not worked well in densely populated, disease-ridden central India. Researchers are now trying to find a vaccine that fits those conditions better. Neal Halsey, of Johns Hopkins University, says the "live" vaccines used commonly today must be backed up with further doses of "inac-tivated" vaccines. These need to become cheaper. The fighting in Afghanistan and Pakistan has hampered vaccination programs there. So have rumors among Muslims in northern Nigeria that the vaccination program was in fact a conspiracy to sterilize children. That allowed the polio virus to strengthen and spread. The Nigerian strain may have now reached a dozen other countries. The final push towards elimination will certainly be costly, though several recent studies suggest that it is cheaper to spend money on a big elimination effort now than to pay the price later for sustained vigilance and health costs. The prospect of a global revival is concentrating minds. That is why, despite the daunting challenges and potential donor fatigue, the world may end up making a go of elimination this time. It can be inferred from the third paragraph that eradication of polio is the hardest in that ______.
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