二尖瓣狭窄病人常出现痰中带血丝的临床表现，其中最可能的因是（）

A.肺动脉高压

B.肺水肿

C.肺梗死

D.合并肺部感染

E.支气管黏膜血管扩张破裂

—________ hours of sports do you do every week?

—Six hours.

A．How long

B．How soon

C．How much

D．How many