◎ 题干
After Jack had sent some e-mails, he _______ working on his project.
A.had started B.has started
C.started D.starts
◎ 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“After Jack had sent some e-mails, he _______ working on his project.A.had started B.has startedC.started D.starts…”主要考查了你对  【一般现在时】【将来进行时】【过去完成进行时】【过去将来时的被动语态】  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。