已知集合P={x|x²≤1}，M={a}，若P∪M=P，则a的取值范围是[ ]

A、(-∞，-1]

B、[1，+∞)

C、[-1，1]

D、(-∞，-1]∪[1，+∞)

The process of growing up is complex for every person, ________ there are many influential factors in a person's growth as well as the development of his personality.

A．but

B．so

C．for

D．therefore