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A,由that 引导的陈述句性的宾语从句，在很多动词如say, think, wish , hope, see, believe, agree, expect, hear , feel等动词后。连词that只起连接作用，在从句中不做句子的成分，也无词汇意义，在口语中常被省略，但在大多数情况下还是以不省为好，特别是在笔语中。
例：I told him that he was wrong.
l在think,believe, suppose, expect等动词引起的宾语从句中，有时谓语尽管是否定意义，却不用否定形式，而将think 等动词变为否定形式。
例：I don’t think you are right. (我认为你做的不对)
l在许多带有复合宾语的句子中，that引导的宾语从句经常移到句子的后面，而用it做形式宾语。
例：We think it wrong that he told a lie to everyone (我认为他向每一个人撒谎是错误的)
B,由连词if、 whether 引导的表示“是否…”的宾语从句。Whether,if 在从句中不做句子的成分，一般情况下，whether和if 可以替换。
例：I don’t know if/whether he will come tomorrow.
The teacher asked if/whether we had finished the experiment.
l在介词后面的宾语从句中不用if引导
例：Everything depends on whether we have enough money。
l宾语从句中有or not时不用if引导.
例：I don’t know whether the movie star will come or not.
l和不定式连用作宾语时不用if引导.
例：Whether to go there or not hasn’t been decided.
C,由wh-引导的宾语从句。连接代词who,whom,whose, what, which,和连接副词when, where, why, how 等连接的宾语从句，它们在句中即有连接从句的作用，又在句中充当句子的成分。
例：Do you know which film they are talking about (which做定语)
I don’t know where he lives. (where 做地点状语)
