when we use metals it is important to know how the

when we use metals it is important to know how the

这个句子的大框是：时间状语从句+形式主语+系动词+表语+作为真正逻辑主语的不定式结构when we use metals时间状语从句to know how they react with different substans这不定式结构做整个句子的逻辑主语is是系动词important是表语还要再细分的话就要拆开每个小句来分析了.先看那个时间状语从句,在这个从句中：when是时间状语从句的引导词,we是这个从句的主语 use是非谓语动词 metals是宾语最后那个不定式：know是非谓语动词 how they react是宾语 with different substans是状语,表伴随======以下答案可供参考======供参考答案1:it 是形式主语，how they react with differet substans是真正意义上的主语，is当然就是谓语了，important 是表语。when we use metals是时间状语供参考答案2:when we use metals / it is important to know / how they /how they react with differet substans /,for example,water and oxygenit 划分句子时间状语从句when we use metals ...主句how they react with differet substans 主语they 谓语react 宾语substan 补语it is important to know

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