A major reason for conflict in the animal world is territory. The male animal【21】______ an

A major reason for conflict in the animal world is territory. The male animal 【21】______ an area. The size of the area is sufficient to provide food for him, his 【22】______ and their offspring. Migrating birds, for example, divide up the best territory in the order of "first come, first 【23】______ " The late arrivals may acquire 【24】______ territories, but less food is 【25】______ , or they are too close to the 【26】______ of the enemies of the species.

When there is conflict over territory, animals will commonly use force, or a 【27】______ of force, to decide which will stay and which will go. It is interesting to note, however, that animals seem to use only the 【28】______ amount of force necessary to drive away the intruder. There is usually no killing. In the 【29】______ of those animals which are capable of doing each other harm, there is a 【30】______ for the losing animal to show the 【31】______ animal that he wishes to submit. When he shows this, the 【32】______ normally stops fighting. Animals (especially birds), which can easily escape from conflict seem to have no 【33】______ against killing, and equally no 【34】______ for 【35】______ . The losing bird simply flies away. However, if two doves age 【36】______ in a cage, and they start fighting, they will 【37】______ to fight until one kills the other. We all think of the dove 【38】______ a 【39】______ of peace and, in its natural habitat, it is peaceful. But the "peace" mechanism does not 【40】______ in a cage.

【21】

A．establishes

B．builds

C．founds

D．erects