这个if从句要用什么时态He is very busy. I don’t know if he _____ or not tomorrow.A. come B. comesC. will come D. is coming【陷阱】此题容易误选B。认为 if 引导的是条件状语从句，从句谓语要用一般现在时表示将来意义。【分析】其实，此题答案应选C，句中if引导的不是条件状语从句(即if≠如果)，而是宾语从句(即if＝是否)，句意为“他很忙，我不知道明天他是否会来。”请看以下类似试题：(1) I don’t know if she _____, but if she ____ I will let you know.A. comes, comes B. will come, will comeC. comes, will come D. will come, comes答案选 D，第一个 if 引导的是宾语从句，第二个 if 引导的是条件状语从句。(2) “When _____ he come?” “I don’t know, but when he _____, I’ll tell you.”A. does, comes B. will, will comeC. does, will come D. will, comes答案选 D，第一个 when 疑问副词，用于引出一个特殊疑问句；第二个 when是从属连词，用于引导时间状语从句。(3) “When he _____ is not known yet.” “But when he ____, he will be warmly welcomed.”A. comes, comes B. will come, will come C. comes, will come D. will come, comes答案选 D，第一个 when 引导的是主语从句，第二个 when引导的是时间状语从句。

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