50. Teachers should be _____ with their students but should not be _____ on them.

A．hard; strict

B．strict; hard

C．hardly; strictly

D．strictly; hardly

动态观察血浓度，可作为检查胎盘功能指标的是（）

A.耐热性酸性磷酸酶

B.雌激素E2

C.缩宫素

D.孕激素

E.绒毛膜促性腺激素