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单选题
Radio check requirement order is （ ） .
A
1. the station being called, 2.A/C call sign, 3. radio check, 4. frequency
B
1. radio check, 2. frequency, 3. A/C call sign, 4. the station being called
C
1. the station being called, 2. frequency, 3. radio check, 4. A/C call sign
D
1. the A/C call sign, 2. the station being called, 3. radio check, 4. frequency
答案解析
正确答案：A
