阅读理解。 All living things on the earth need other living things to live with. 1 Sometimes one living thing kills another. Each kind of life eats another kind of life in order to live, and together they form a food chain (食物链). 2 while others are not. But all food chains begin with the sun, and all food chains become broken if one of the links disappears. All life needs sunlight to live on. 3 They make food from sunlight, water, air and so on. 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. 4 We are members of many food chains. We eat wheat, rice, vegetables, fruit and so on. We also eat meat and drink milk. But people often break up the food chains. They kill wild animals. They also make rivers, lakes and seas dirty. 5 the fish in them cannot be killed. If people eat the fish, they will get strange diseases. Each form of life is linked to all the others. Breaking the links puts all life in danger. A. When these rivers, lakes and seas are polluted, B.  But only plants can use sunlight directly. C.  Some food chains are simple, D. What about human beings? E.  Nothing lives alone.