The best title for this passage would be ______.

A．the emotional origin of the war in Ireland is lost in time
B．historically, we have created an "us" versus "them" society
C．humans have had a natural disinclination toward formal grouping
D．the First World War is an example of how man has always avoided domination

A．games are psychologically unhealthy
B．any artificially-created subspecies would be our enemy
C．the artificial creation of a subspecies unlike us is something that never happens
D．the real or imagined existence of an opposing subspecies is inherent in man's activities