—I called on you but you were not in last night.

—Because I ________ supper with my parents in a restaurant. [ ]

A. has had       

B. had    

C. was having    

D. had had

突触前抑制是由于突触前膜（）

A．产生超极化

B．释放抑制性递质

C．递质耗竭

D．兴奋性递质释放减少

E．产生抑制性突触后电位