题目内容
A．The change of life-style.B．The change of the nature of occupations.C．The increase of
查看答案
搜索结果不匹配？点我反馈
更多问题
Section B
Directions: In this section, you will hear 3 short passages. At the end of each passage, you will hear some questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A, B, C and D.
听力原文： Are you afraid to raise your hand in class, even when you know the answer？ If you are, most people would say that you're shy.
If you feel shy, you're not alone. Nine out of ten people are at least a little shy. But however shy you are, scientific evidence seems to show that it isn't your fault. You may have been born that way.
How do psychologists measure shyness？ One way is by observation. They keep detailed records of people's actions—like how often these people speak to others, or how long it takes someone to say hello to a stranger,
Another way to measure shyness is to ask people questions. The test only takes about 10 minutes. It asks questions like "Do you like going out a lot？" and "Do you have many friends？" People must answer either yes or no. These questions can predict how people actually behave in social situations. Suppose the test tells you that someone is shy, chances are good that that person will act shy.
When scientists measure shyness, they're really comparing degrees of shyness. In other words, when researchers say people are shy, they really mean they are shyer than others.
(27)
Wildfires
In just seconds, a spark or even the sun's heat alone sets off an extremely large fire. The wildfire quickly spreads, consuming the thick, dried-out plants and almost everything else in its path. What was once a forest becomes a virtual powder keg of untapped fuel. In a seemingly instantaneous burst, the wildfire overtakes thousands of acres of surrounding land, threatening the homes and lives of many in the vicinity.
Fire Starters
On a hot summer day, when drought conditions peak, something as small as a spark from a train car's wheel striking the track can ignite a raging wildfire. Sometimes, fires occur naturally, ignited by heat from the sun or a lightning strike. However, the majority of Wildfires are the result of human carelessness.
Common causes for wildfires include:
Arson
Campfires
Discarding lit cigarettes
Improperly burning debris
Playing with matches or fireworks
Prescribed fires
Everything has a temperature at which it will burst into flames. This temperature is called a material's flash point. Wood's flash point is 572 degrees Fahrenheit(300 ℃). When wood is heated to this temperature, it releases hydrocarbon gases that mix with oxygen in the air, combust and create fire.
There are three components needed for ignition and combustion to occur. A fire requires fuel to burn, air to supply oxygen, and a heat source to bring the fuel Up to ignition temperature. Heat, oxygen and fuel form. the fire triangle. Firefighters often talk about the fire triangle when they are trying to put out a blaze. The idea is that if they can take away any one of the pillars of the triangle, they can control and ultimately extinguish the fire.
After combustion occurs and a fire begins to burn, there are several factors that determine how the fire spreads. These three factors include fuel, weather and topography. Depending on these factors, a fire can quickly fizzle or turn into a raging blaze that scorches thousands of acres.
Fueling the Flames
Wildfires spread based on the type and quantity of fuel that surrounds it. Fuel can include everything from trees, underbrush and dry grassy fields to homes. The amount of flammable material that surrounds a fire is referred to as the fuel load. Fuel load is measured by the amount of available fuel per unit area, usually tons per acre.
A small fuel load will cause a fire to burn and spread slowly, with a low intensity. If there is a lot of fuel, the fire will burn more intensely, causing it to spread faster. The faster it heats up the material around it, the faster those materials can ignite. The dryness of the fuel can also affect the behavior. of the fire. When the fuel is very dry, it is consumed much faster and creates a fire that is much more difficult to contain.
Here are the basic fuel characteristics that decide how it affects a fire:
Size and shape
Arrangement
Moisture content
Small fuel materials, also called flashy fuels, such as dry grass, pine needles, dry leaves, twigs and other dead brush, burn faster than large logs or stumps(this is why you start a fire with kindling rather than logs). On a chemical level, different fuel materials take longer to ignite than others. But in a wildfire, where most of the fuel is made of the same sort of material, the main variable in ignition time is the ratio of the fuel's total surface area to its volume. Since a twig's surface area is much larger than its volume, it ignites quickly. By comparison, a tree's surface area is much smaller than its volume, so it needs more time to heat up before it ignites.
As the fire progresses, it dries out the material just beyond it—heat and smoke approaching potential fuel causes the fuel's moisture to
Wildfires are mainly caused by people, not by nature.
A．how learnedB．how to learnC．to how learnD．how learning
微信支付 
支付宝支付