The government has taken some measures to solve the shortage of electricity, but it may be some time _______ the situation improves.
A.since
B.when
C.unless
D.before
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D解析考查连词用法。“It be+一段时间+before…”是固定结构，该结构的意思是“要过……（长）时间才……”。when“．．．．．．的时候”；since“从．．．．．．开始”；unless“除非”；根据题意D最佳。