A suitable title for this passage would be ______.

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

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