All living things on the earth need other living things to live.Nothing lives alone.Most animals must live in a group,and even a plant grows close together with others of the same kind.Sometimes one living thing kills another,or one eats and the other is eaten.One kind of life eats another kind of life in order to live,and together they form a food chain .All food chains begin with the sun,and all food chain become broken up if one of them disappears. All life needs sunlight to live on.But only plants can use sunlight directly.Plants are"factories".They make food from sunlight,water and things in the soil and air. Plants 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,and others eat smaller animals.Meat-eating animals are only eating plants indirectly. What about human beings?We are members of any food chain.We eat rice,vegetables,fruits and so on.We also eat meat.But men often break up the food chain.They kill wild animals.They also make rivers,lakes and seas dirty.When these rivers,lakes and seas are polluted,the fish in them cannot be eaten.If men eat the fish,they will get strange diseases. Each form of life is linked to all others.Breaking the links puts all life in danger. Which can change the sun's energy into food?
Plants. Humans. Plant-eating animals. Meat-eating animals.