问题
选择题
It hasn't been made clear ________ the new underground line is to be open to traffic.
A．when
B．that
C．what
D．where
答案
答案：A
A 考察名词性从句。这是when引导的主语从句，it是形式主语。句意：新的地铁线路何时开放还不清楚。故A正确。
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