— What's wrong with your uncle, Jack? 　　　　

— He is ill. A doctor ______. [ ]

A. has to look for　　　　　　　　　

B. is being operated on 　　

C. must ask for　　　　　　　　　　

D. has just been sent for

有机磷中毒时，可使（）

A.乙酰胆碱释放增加

B.乙酰胆碱释放减少

C.胆碱酯酶活性增加

D.胆碱酯酶活性减少

E.骨骼肌终板处的乙酰胆碱受体功能障碍