We also had different students in some classes, so ______was a struggle to remember all the faces.

A．it

B．this

C．that

D．one

下列具有降压作用的有效成分，错误的是（）

A.川芎嗪

B.麻黄碱

C.去甲乌药碱

D.山楂总黄酮

E.三七总皂苷