下列哪项引起左室容量负荷过重
A．二尖瓣狭窄
B．二尖瓣关闭不全
C．肥厚型心肌病
D．主动脉瓣狭窄
E．肺动脉高压
参考答案：B
--Listen! Someone is knocking at the door.
-- ______ be Mary. She has just been to Beijing
A．She mustn’t
B．It can’t
C．It must
D．She may
