x4+x2-2．
x4+x2-2，
=（x2+2）（x2-1），
=（x2+2）（x+1）（x-1）．
It's cold. you'd better _____ more clothes.[ ]
A. put on
B. wear
C. to put on
国际长途电话号码的字冠是（）。
A、00
B、0
C、1
D、8
