The phrase “if not possible, advise” may be used together with t

The phrase “if not possible, advise” may be used together with the clearance or instruction _______ .

A.when the controller is in doubt about the capability of the pilot in complying with the clearance or instruction

B.after an alternative clearance or instruction is offered

C.if the controller is sure that the pilot cannot comply with the clearance or instruction

D.when the controller is not ready to help the pilot

正确答案是A