Professor James will give us a lecture on the Western culture, but when and where _______ yet.

A．hasn’t been decided

B．haven’t decided

C．isn’t being decided

D．aren’t decided

对于1发失效的轻型双发飞机，什么时候可以允许侧滑仪的显示球偏离到参考线之外？（）

A.当以最小操纵速度进行机动飞行时避免坡度太大

B.当以任何大于最小操纵速度的速度飞行时

C.当以有坡度的姿态练习临界失速时