A major reason for conflict in the animal world is territory. The male animal【C1】______ an

area. The size of the area is【C2】______ to provide food for him, his【C3】______ and their offspring. Migrating birds, for example, divide up the best territory in the order of "first come, first【C4】______ "The late arrivals may acquire【C5】______ territories, but less food is available, or they are too close to the【C6】______ of the enemies of the species.

When there is【C7】______ over territory, animals will commonly use force, or a【C8】______ of force, to decide which will stay and which will go. It is interesting to note,【C9】______ ,that animals seem to use only the【C10】______ amount of force necessary to drive away the intruder. There is usually no killing. In the【C11】______ of those animals which are capable of doing each other harm, there is a【C12】______ for the losing animal to show the winning animal that he wishes to submit. When he shows this, the【C13】______ normally stops fighting. Animals (especially birds),which can【C14】______ escape from conflict seem to have no【C15】______ against killing, and equally no mechanism for【C16】______ The losing bird simply flies away. However, if two doves are 【C17】______ in a cage, and they start fighting, they will continue to fight until one kills the other. We all think of the dove as a【C18】______ of peace and,【C19】______ its natural habitat, it is peaceful. But the "peace" mechanism does not【C20】______ in a cage.

【C1】

A．establishes

B．builds

C．founds

D．erects