21.Soils
    There are many different kinds of soils. Different soils have different types of rock and minerals in them. Some soils have more water in them than others. Some soils might have more plant and animal material in them, too. Different kinds of soils are found in different parts of the world. There are several kinds of soils found in the United States. In some areas, the soil has a lot of clay. Other soils are very sandy. Loam is a kind of soil that has a good mixture of clay and sand. In some places, soil layers are very thick. Lots of plants grow in places with a thick soil layer. In dry and windy places soil layers are much thinner. Layers of soil on mountains are thin because gravity pulls the soil downhill. The type of soil in a particular place affects what kinds of plants can grow there.
22. Crisis
    Life is a contest! Who will win? A bluebird and sparrow both compete for space to build their nests. A fast-growing maple tree and slower-growing dogwood compete for the sunlight they both need. Oil competes with coal and nuclear power as an energy source for electric p
ower plants! There is a problem. There is a limited amount of space for birds, sunlight for trees, and energy for people! If we do not cut back on our uses of some of our resources, someday they will be gone! How can we use energy today and know we will have enough to go around in the future? We can choose alternate, or replacement, energy resources. It takes the earth millions of years to create coal, oil, and gas. They are nonrenewable resources. Solar energy, wind energy and water energy are renewable resources. It takes the earth millions of years to create coal, oil, and gas. They are nonrenewable resources. Solar energy, wind energy and water energy are renewable. What other ways can we conserve our resources? How can we make sure there is always enough to go around?
23.  America’s Worst Surprise
    December 7, 1941 was one of the worst days in American history. Nearly all Americans who are old enough to remember that day can still remember what they were doing at the moment they heard “the news”. The news was that America had been attacked! Shortly before 2:00 P.M., a radio dispatch came into Washington from Honolulu, Hawaii. “Air Raid,
Pearl Harbor— This is no drill.” Japanese planes had begun an attack on the largest American military base in the Pacific. They first destroyed planes on the ground. Then they bombed the ships in the harbor. No one had expected the attack. So no one was prepared for it. And it did not take long for Japanese to do their damage. When the smoke cleared, the Navy counted its losses. Eighteen ships had been sunk or badly damaged. Nearly 150 planes had been destroyed. More than 2,400 Americans had been killed and more than 1,200 wounded.
24. Great Depression in the U.S.
In 1929, the bills started to come in. American industry had produced too many goods. Americans could not afford to buy all of them. So factories had to cut down on their production. Many workers lost their jobs. Investors tried to get their money back. But businesses did not have enough money to pay them. Banks tried to get their money back from investors. But the investors could not pay, either. Too many people owed money. And few of them could pay their bills. 四级听力During the next few years, business got worse and worse.
By 1932, banks all over the country were closing. People without money could not buy goods. So more businesses closed. More and more people lost their jobs. By 1932, more than 12 million Americans were jobless. Millions more were earning barely enough to live on. The country was in a great depression they had never experienced before.
25. A Place of Our Own
    We are all usually very careful when we buy something for the house. Why? Because we have to live with it for a long time. We paint a room to make it brighter, so we choose the colors carefully. We buy new curtains in order to match the newly decorated room, so they must be the right color. We move the furniture round so as to make more space—or we buy new furniture—and so on. It is an endless business. Rich or poor, we take time to furnish a room. Perhaps some people buy furniture in order to impress their friends. But most of us just want to enjoy our surroundings. We want to live as comfortably as we can afford to. We spend a large part of our lives at home. We want to make a small corner in the world which we can recognize as our own.
26. Travel for Work
    You can see them in every airport in the world. They are businessmen and women who have to travel for their work. When they first applied for the job, they may have thought of good food and hotels, huge expense accounts and fashionable cities. Now they have to sit in airport lounges, tired and uncomfortable in their smart clothes, listening to the loudspeaker announce “The fight of Tokyo, or Berlin, or New York is delayed for another two hours.” Some people say to me, “How lucky you are to be able to travel abroad in your work! You can go sightseeing without paying any money by yourself!” They think that my job is like a continual holiday. It is not. There are advantages, of course, and I do thin I am lucky, but only because I can go to places I would never visit if I was a tourist.