单选题
A major reason for conflict in the animal world is
territory. The male animal{{U}} {{U}} 1 {{/U}} {{/U}}an area.
The size of the area is sufficient to provide food for him, his{{U}}
{{U}} 2 {{/U}} {{/U}}and their offspring. Migrating birds, for
example, divide up the best territory in the order of "first come,
first{{U}} {{U}} 3 {{/U}} {{/U}}" The late arrivals may
acquire{{U}} {{U}} 4 {{/U}} {{/U}}territories, but less food
is{{U}} {{U}} 5 {{/U}} {{/U}}, or they are too close to
the{{U}} {{U}} 6 {{/U}} {{/U}}of the enemies of the
species. When there is conflict over territory, animals will
commonly use force, or a{{U}} {{U}} 7 {{/U}} {{/U}}of force, to
decide which will stay and which will go. It is interesting to note, however,
that animals seem to use only the{{U}} {{U}} 8 {{/U}}
{{/U}}amount of force necessary to drive away the intruder. There is usually no
killing. In the{{U}} {{U}} 9 {{/U}} {{/U}}of those animals which
are capable of doing each other harm, there is a {{U}}{{U}} 10
{{/U}} {{/U}}for the losing animal to show the{{U}} {{U}} 11
{{/U}} {{/U}}animal that he wishes to submit. When he shows this, the{{U}}
{{U}} 12 {{/U}} {{/U}}normally stops fighting. Animals (especially
birds), which can easily escape from conflict seem to have no{{U}} {{U}}
13 {{/U}} {{/U}}against killing, and equally no{{U}} {{U}}
14 {{/U}} {{/U}}for{{U}} {{U}} 15 {{/U}} {{/U}}. The
losing bird simply flies away. However, if two doves age{{U}} {{U}}
16 {{/U}} {{/U}}in a cage, and they start fighting, they will{{U}}
{{U}} 17 {{/U}} {{/U}}to fight until one kills the other. We all
think of the dove{{U}} {{U}} 18 {{/U}} {{/U}}a{{U}}
{{U}} 19 {{/U}} {{/U}}of peace and, in its natural habitat, it is
peaceful. But the "peace" mechanism does not{{U}} {{U}} 20
{{/U}} {{/U}}in a cage.