◎ 题干
They kept trying _____ they must have known it was hopeless.
A.ifB.becauseC.whenD.where
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“They kept trying _____ they must have known it was hopeless.A.ifB.becauseC.whenD.where…”主要考查了你对  【并列连词】【从属连词】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。