1. 引导主语从句并在句首时不用if。如： Whether we go there is not decided. 我们是否去那里还没决定。 2. 引导表语从句时不用if。如： The question is whether we can get there on time. 问题是我们能否按时到达那里。 3. 引导同位语从句时不用if。如：
英语句子成分讲解 一、主语（subject）: 句子说明的人或事物。 The sun rises in the east. (名词) He likes dancing. (代词) Twenty years is a short time in history. (数词) Seeing is believing. (动名词) To see is to believe. (不定式) What he need
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