专四
A．must have been
B．will be
C．were
D．has been
考查情态动词表示推测的用法。由本句中for引导的原因状语从句(时态为一般过去时)可以判定，主句是表示对过去事情的肯定推测，需用“must have+过去分词”的结构，故本题选A。
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A．to deprive
B．deprived
C．depriving
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A．since he became
B．would he become
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A．based
B．basing
C．to base
D．to be based
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根据以下资料，回答题：
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