问题
单项选择题
The frequency（）the safety message will be transmitted shall be included in DSC safety call.
A.which
B.on which
C.at which
D.in which
答案
参考答案：B
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The frequency（）the safety message will be transmitted shall be included in DSC safety call.
A.which
B.on which
C.at which
D.in which
参考答案：B