胸外心脏按压的“胸泵机制”是（）。

A.压迫心室，将血液驱入主动脉和肺动脉

B.压迫大血管，促使血液形成循环

C.压迫心脏使心房内压力升高，促使血液形成循环

D.压迫心房，促使血液形成循环

E.胸内压升高使各心腔和血管内压力升高，驱动血液循环

—How many _____ teachers are there in your school? 

— _____ them _____ over two hundred. [ ]

A. woman; The number of; is

B. women; The number of; is

C. woman; A number of; is

D. women; A number of; are