HF的天线耦合器安装于（）
A.垂尾
B.水平尾翼
C.电子设备舱
D.后货舱
参考答案：A
— Have you ever visited the Opera House?
—Yes．When I was in Sydney, I ______ it twice．
A．have visited
B．visited
C．had visited
D．would visit
实践是物质性的活动，具有间接现实性。( )
