脑膜炎球菌侵入机体繁殖后，因自溶或死亡而释放内毒素，内毒素的主要作用是引起

A.菌血症 

B.血小板解聚 

C.血液白细胞减少 

D.细菌素产生 

E.血管坏死和血栓形成，周围血管出血 

Don’t talk loudly at the meeting. If you ________, you will have to leave.

A. do                      B. are                       C. did