题目内容
Black HolesMost 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. 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 are part of space.（）
查看答案
搜索结果不匹配？点我反馈
更多问题
第二篇Good Table MannersManners play an important part in making a favorable impression at the dinner table. Here are some general rules:Napkin (餐巾) useThe meal begins when the host unfolds his or her napkin. This is your signal to do the same, so place your napkin on your lap. Unfold it completely if it is a small napkin, or in half, lengthwise (纵向地), if it is a large dinner napkin.If you need to leave the table during the meal, place your napkin on your chair as a signal to your server that you will be returning. Once the meal is over, place your napkin neatly on the table to the right of your dinner plate. Do not refold it.Use a napkin only for your mouth. Never use it for your nose, face or forehead.Use of utensils (餐具)Start with the knife, fork or spoon furthest from your plate, and work your way in, using one utensil for each course.If soup is served, remember to spoon away from yourself. This helps stop the drips. Do not put the entire soup spoon in your mouth. Instead, fill a soup spoon about 75 per cent with soup, and sip (啜饮) it from the side noiselessly.After finishing dinner, place the knife and fork parallel to one another across the Plate with the knife alade facing inward toward the plate.Using your f’ingersHere’s a list of finger foods: sandwiches, cookies, small fruits or berries with stems, French fries and potato chips, hamburgers.Chew(咀嚼) with your mouth closed and don’t make noise; don’t talk with your mouth full.Bread must be broken with your hands. It is never cut with a knife.Don’t pick something out of your teeth. Instead, excuse yourself to the bathroom.If possible, try not to cough at the table.Do not put your elbows(肘) on the table. In France, it is essential to have both hands above the table at the same time.Do not put bones or anything else on the table. Things that are not eaten should be put on your plate. Which of the following shows good table manners（）
An Intelligent CarDriving needs sharp eyes, keen ears, quick brain, and coordination(协调) between hands and the brain. Many human drivers have all (51) and can control a fast-moving ear. But how does an intelligent car control itself?There is a virtual(虚拟) driver in the smart car. This virtual driver has "eyes", "brains", "hands" and "feet" too. The minicameras (52) each side of the ear are his "eyes" which (53) the road conditions ahead of it. They watch the (54) to the car’s left and right. There is also a highly automatic driving (55) in the car. It is the built-in computer, which is the virtual driver’s "brain". His "brain" (56) the speeds of other moving cars near it and analyzes their positions. Basing on this information, it chooses the (57) path for the intelligent ear, and gives instructions to the "hands" and "feet" to act accordingly. In this way, the virtual driver (58) his car.What is the virtual driver’s best advantage He reacts (59) . The minicameras are bringing (60) continuously to the "brain". It completes the processing of the images with-in 100 milliseconds. (61) , the world’s best driver needs at least one second to react. Besides, when he takes (62) , he needs one more second.The virtual driver is really wonderful. He can reduce the accident (63) considerably on expressways(高速公路). In this (64) , can we let him have the wheel at any time and in any place Experts (65) that we cannot do that just yet. His ability to recognize things is still limited. He can now only drive an intelligent car on expressways. 60（）
A. How does DNA workB. What is the Human Genome Project aboutC. How are the DNA samples collectedD. What are the goals of the Human Genome ProjectE. What is the role of each geneF. What are the consequences of genetic mutations Paragraph 1（）
Farmers’ MarketsCharlotte Hollins knows she faces a battle. The 23-year-old British farmer and her 21-year-old brother Ben are fighting to save the farm from developers that their father worked on since he was 14. (46) "You don’t often get a day off. Supermarkets put a lot of pressure on farmers to keep prices down. With fewer people working on farms it can be isolating, "she said. " There is a high rate of suicide and farming will never make you rich!"Oliver Robinson, 25, grew up on a farm in Yorkshire. (47) "I’m sure dad hoped I’d stay, "he said. "I guess it’s a nice, straightforward life, but it doesn’t appeal. For young, ambitious people, farm life would be a hard world. "For Robinson, farming doesn’t offer much "in terms of money or lifestyle. "Hollins agrees that economics stops people from pursuing farming rewards: "providing for a vital human need, while working outdoors with nature. "Farming is a big political issue in the UK. (48) The 2001 foot and mouth crisis closed thousands of farms, stopped meat exports, and raised public consciousness of troubles in UK farming.Jamie Oliver’s 2005 campaign to get children to eat healthily also highlighted the issue. This national concern spells (带来) hope for farmers competing with powerful supermarkets. (49) "I started going to Farmers’ Markets in direct defiance (蔑视)of the big supermarkets. (50) It’s terrible, "said Londoner Michael Samson.A. But he never considered staying on his father and grandfather’s land.B. While most people buy food from the big supermarkets, hundreds of independent Farmers’ Markets are becoming popular.C. While confident they will succeed, she lists farming’s many challenges.D. Young people prefer to live in cities.E. I seriously objected to the super-sizing of everything what exactly do they put on our apples to make them so big and red7F. "Buy British" campaigns urge(鼓励)consumers not to buy cheaper imported foods. 49（）
微信支付 
支付宝支付