To avoid confusion, the ATC unit should, if appropriate, identify the aircraft which will______ to change its call sign by referring to its position and/or level.
A.instruct
B.have been instructed
C.have instructed
D.be instructed
正确答案是D
To avoid confusion, the ATC unit should, if appropriate, identify the aircraft which will______ to change its call sign by referring to its position and/or level.
A.instruct
B.have been instructed
C.have instructed
D.be instructed
正确答案是D