All living things on the earth need other livingthings to live. Nothing lives alone. Most animalsmust live in a group, and even a plant grows closetogether with others of the same kind. Sometimesone living thing kills another, one eats and the otheris eaten. Each kind of life eats another kind of lifein order to live, and together they form a foodchain(食物链).Some food chains become brokenup if one of the links disappears.