过敏性紫癜出血原因是（）

A.血小板数量减少

B.多种凝血因子消耗

C.血管壁异常

D.凝血因子合成障碍

E.遗传性凝血因子缺乏

The students __________ loudly when the teacher came in.[ ]

A. talked

B. talking

C. were talking

D. to talk