A major mason for conflict in the animal world is territory. The male animal【C1】______an a

rea. The size of the area is sufficient to provide food for him, his【C2】______and their offspring. Migrating birds, for example,【C3】______up the best territory in the order of "first come, first【C4】______". The late arrivals may acquire【C5】______ territories, but【C6】______food is available, or they are too close to the【C7】______of the enemies of the species.

When there is conflict 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【C12】______doing each other harm, there is a【C13】______for the losing animal to show the winning animal that he wishes to submit.

When he shows this, the【C14】______normally stops fighting. Animals(especially birds),【C15】______can easily escape from conflict seem to have no【C16】______against killing, and equally no mechanism for【C17】______. The losing bird simply flies away. However, two pigeons are placed in a cage, and they start if fighting, they will continue to fight【C18】______one kills the other. We all think of the pigeon as a【C19】______of peace and, in 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