强心苷治疗心力衰竭的主要药理作用是

A．降低心肌耗氧量

B．正性肌力作用

C．使已扩大的心室容积缩小

D．减慢心率

E．减慢房室传导

A．(A) They were boring.

B．(B) They were good lecturers.

C．(C) They seldom asked questions.

D．(D) They talked too much in class.