When the weather at the landing airport or alternate airport is _______ , a second alternate airport is to be specified.
A.below minimum
B.at marginal level
C.changeable
D.unavailable
正确答案是B
When the weather at the landing airport or alternate airport is _______ , a second alternate airport is to be specified.
A.below minimum
B.at marginal level
C.changeable
D.unavailable
正确答案是B