心室肌的有效不应期较长，一直延续到（）
A.收缩期开始
B.收缩期中间
C.舒张期开始
D.舒张期结束
E.舒张期结束以后
参考答案：C
--- Did you catch the train to Beijing last night?
--- No. It ______ for ten minutes by the time I got to the station.
A．has left
B．had left
C．has been away
D．had been away
哪些是分娩期导致心脏负担加重的原因（）
A.中心静脉压升高
B.左向右分流
C.外周循环阻力增加
D.肺循环阻力增加
E.回心血量骤增
