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  3. Everything living on earth--plants and animals need other living things. Nothing lives alone. Most animals must live in a group,

Everything living on earth--plants and animals need other living things. Nothing lives alone. Most animals must live in a group,

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问题    Everything living on earth--plants and animals need other living things. Nothing lives alone. Most animals must live in a group, and even a tree or a plant grows close together with others of the same kind. Sometimes one living thing hunts another; one eats and the other is eaten. Each kind of life eats another kind of life in order to live, and together they form a food chain. Some food chains are simple; others are complicated. But all have two things in common--all food chains begin with the sun, and all food chain become broken up if one of the links disappears. All life depends on energy from sunlight. Only plants can use this energy directly. Their leaves are little factories that use sunlight to make food from water and things in the soil and air.    Plants in turn feed all other living things. Animals can only use the sun’s energy after it has been changed into food by plants. Some animals feed directly on plants; others eat smaller animals. Meat-eating animals are only eating plants indirectly.
   What about human beings.’? We are members of many food chains. We eat wheat, rice, vegetables, fruit and so on. We also eat meat and drink milk. This means the sun’s energy passes through plant to animal before it reaches us.
   Nature is a greater thing. Any food chain always produces enough for each of its members if it is left alone. When there isn’t enough food for any link in chain, some of its members die off. So the balance is broken up.
   But men in their greed and ignorance often break up the food chain and do great harm not only to one plant or animal, but to all the links irt the chain. People make seas and rivers dirty. They destroy whole forests and kill many kinds of wild animals and birds. When a river becomes dirty, the fish can’t be eaten. Men eat the fish and get strange disease. In some places men have no fish to eat any more, because the fish have died off. Each form of life is linked to all others. Breaking the links puts all life in danger.
Why is all life in danger? Because ______ break up the food chains.
选项 A、Human beings
B、animals
C、plants and animals
D、man and wild animals
答案A
解析
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