B

    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 , 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（食物链）. Some food chains are simple , while others are not . But all food chains begin with the sun , and all food chains become broken up if one of the links 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 （能量）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 , fruits and so on . We also eat meat and drink milk . But men often break up the food chains . They kill wild animals . They also make rivers , lakes and seas dirty . When these rivers , lakes and seas are polluted , the fish in them can not 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.

  46. How does every living thing on the earth live ?

    A. Each plant can live alone.

    B. Each animal can live alone.

    C. If living things want to live , they must kill each other.

    D. Every living thing on the earth cannot live without others.

  47. Which living things can use the sun’s energy directly ?

    A. Animals.                     B. Plants    C. Both animals and plants           D. All living things.