【正文】 waves can. That is why you can hear people talking in another room even though you cannot see them. The energy of some waves is destructive. An earthquake produces seismic waves. Catch a wave. Ask a friend to stand a few feet away from you. Stretch a spring between you. Shake the spring to transfer energy to it. What happens? The spring bounces up and down in waves. When the waves reach your friend, they bounce back to you!Light waves travel 300,000 kilometers (186, 000 miles) per second! They can also travel through a vacuum. That is why light from the sun and distant stars can travel through space to the earth! (175 words)Useful Words and Expressions:matter n．物質(zhì)；內(nèi)容；事情reading matter閱讀材料This is a matter of no account．這是一件無關(guān)緊要的事。I have an urgent matter to attend to．我有一件急事要辦。I have an important matter to talk to you about．我有件重要的事要和你談?wù)?。destructive adj．破壞（性）的seismic adj．［地］地震的seismic waves震波bounce v．（使）反跳，彈起bounce back彈回vacuum n．真空Passage 21SoilsThere 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. (150 words)Useful Words and Expressions:mineral n．礦物，礦石clay n．黏土，泥土loam n．（含有黏土、沙以及有機(jī)物質(zhì)的）肥土layer n．層，階層gravity n．地心引力，重力downhill adv．往下affect v．影響；感動；患（?。?，中（暑）be affected by heat［cold］中暑［著涼〕Smoking affect health．吸煙影響健康。He was deeply affected by my words．他聽了我的話很受感動。Passage 22CrisisLife is a contest! Who will win? A bluebird and sparrow both pete for space to build their nests. A fastgrowing maple tree and slowergrowing dogwood pete for the sunlight they both need. Oil petes with coal and nuclear power as an energy source for electric power 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. What other ways can we conserve our resources? How can we make sure there is always enough to go around? (159 words)Useful Words and Expressions:bluebird sparrow n．[鳥]麻雀pete for為……競爭maple n．［植］楓，楓木dogwood n．山茱萸nuclear power n．核動力power plant n．發(fā)電廠，發(fā)電站alternate n．替換物replacement n．代替者；替換物nonrenewable resources不可再生資源conserve vt．保存，保藏conserve one39。s strength 保存力量conserve our national heritage in the face of bewildering change在面臨令人手足無措的改變時，要保護(hù)我們的民族遺產(chǎn)Passage 23America39。s Worst SurpriseDecember 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 ., 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 the 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. (157 words)Useful Words and Expressions:dispatch ，急件air raid Pearl Harbor珍珠港Drill n．軍事訓(xùn)練，操練Military adj．軍事的，軍用的，軍人的military base軍事基地a military bearing 軍人的氣度military attire軍人的服裝military service兵役military operations軍事行動bomb n．炸彈Vt．投彈于，轟炸Sink Vi．（使）下沉sunk sink的過去分詞和過去式 Passage 24Great Depression in the In 1929, the bills started to e 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.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. (151 words)Useful Words and Expressions:bill n．賬單，票據(jù)foot the bill 付賬；負(fù)責(zé)cut down on減少investor n．投資者barely adv．僅僅，剛剛be barely of age剛成年a barely furnished room陳設(shè)簡陋的房間He barely escaped.．他好不容易地才逃了出來。live on v．繼續(xù)生活，靠……生活depression n．沮喪，蕭條Great Depression 大蕭條Passage 25A Place of Our OwnWe 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 colours caref