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．car pooling must be studied
B．rapid mass transit system must be introduced
C．flexible work hours must be experimented
D．overall strategies must be coordinated