问题
单项选择题
VHF Radio is one of the very important navigational instruments on board，（）messages can be sent.
A.by which
B.through which
C.by that
D.through that
答案
参考答案：B
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VHF Radio is one of the very important navigational instruments on board，（）messages can be sent.
A.by which
B.through which
C.by that
D.through that
参考答案：B