What are you doing out of bed ,Tom? You are         to be asleep.

A．supposed

B．known

C．thought

D．considered

引起前置胎盘的主要危险因素为（）。

A.剖宫产史

B.子宫手术史

C.子宫先天畸形

D.子宫肌瘤

E.多产史