You should be careful of such a person          flatters you in your presence and speaks ill of you in behind.

A．who

B．that

C．as

D．which

孕妇需避免X线检查，是因为

A．X线的光化学作用

B．X线的荧光作用

C．X线的生物作用

D．X线的感光作用

E．以上都不是