Most animals have little (connect) with animals of different kind， they hunt them for food. Sometimes，however，two kinds of 48. (animal) come together in a partnership(伙伴关系), does good to both of them .You may have noticed some birds (sit) on the backs of sheep. This is not because they want a ride，but because they find easy food in the parasites (寄生虫) on sheep. The sheep allow the birds (do) so because they remove the cause of discomfort. So although they can manage without each other，they do (good) together.
Sometimes an animal has a plant partner. The relationship develops until the two partners cannot manage without each other. is this in the corals (珊瑚) of the sea. In their skins they have tiny plants act as "dustman"，taking some of the waste products from the coral and giving in return oxygen (氧气) which the animal needs to breathe. If the plants (kill)，or are even prevented light so that they cannot live normally, the corals will die.
