写作中常需要变换句式，以避免句式的雷同。例如“从句”变成“非谓语动词结构”有如下几种情况：
1. 有些名词性从句可以减化为不定式，例：
①I don‘t know where I should go.
→ I don’t know where to go．（宾语从句简化为不定式）
②Where I should go hasn’t been decided.
→Where to go hasn’t been decided.（主语从句简化为不定式）
③The question is where I should go.
→The question is where to go.（表语从句简化为不定式）
像what to do、when to leave、how to do it等形式都属于这种情况。
2. 有些状语从句可以同时省略主语和be动词，简化为“引导词+分词”的形式，例：
When he was wondering in the street, he saw the accident.
→When wondering in the street, he saw the accident.
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