三尖瓣位于
A．左房室口 B．右房室口C．肺动脉口 D．主动脉口E．冠状动脉口
参考答案：B
The couple work in their garden every morning, ______ for a weight loss.
A．hoping
B．hoped
C．to hope
D．hope
无源滤波器的优点有哪些？
