There was a strange sound outside. Mary went out and _____ around, but she _____ nothing. [ ]

A. looked; saw

B. saw; saw

C. watched; looked

D. looked; find

当着陆飞机飞在下滑面以上时，则下滑指示显示（）。

A.90Hz占优

B.150Hz占优

C.两者相等

D.不能确定