狀語從句指句子用作狀語時(shí),起副詞作用的句子.它可以修飾謂語、非謂語動(dòng)詞、定語、狀語或整個(gè)句子.
　　根據(jù)其作用可分為時(shí)間、地點(diǎn)、原因、條件、目的、結(jié)果、讓步、方式和比較等從句.狀語從句一般由連詞(從屬連詞)引導(dǎo),也可以由詞組引起.從句位于句首或句中時(shí)通常用逗號與主句隔開,位于句尾時(shí)可以不用逗號隔開.
　　考點(diǎn)聚焦
　　1、時(shí)間狀語從句
　　(1)as、when、while用
　　as表示"當(dāng)……的時(shí)候",往往和when/ while通用,但它著重強(qiáng)調(diào)主句與從句的動(dòng)作或事情同時(shí)或幾乎同時(shí)發(fā)生.
　　She came up as I was cooking.(同時(shí))
　　The runners started as the gun went off.(幾乎同時(shí))
　　when:(at or during the time that )既可以表示在某一點(diǎn)的時(shí)候,又可表示在某一段時(shí)間內(nèi),主句與從句的動(dòng)作或事情可以同時(shí)發(fā)生也可以先后發(fā)生.
　　It was raining when we arrived.(指時(shí)間點(diǎn))
　　When we were at school, we went to the library every day.(在一段時(shí)間內(nèi))
　　while意思是"當(dāng)……的時(shí)候"或"在某一段時(shí)間里".主句中的動(dòng)作或事情在從句中的動(dòng)作或事情的
　　進(jìn)展過程中發(fā)生,從句中的動(dòng)詞一般要用延續(xù)性動(dòng)詞.在when表示a period of time時(shí),兩者可以互換.
　　Please don't talk so loud while others are working.
　　He fell asleep while/when reading. Strike while the iron is hot.(用as或when不可,這里的while意思是"趁……")
　　(2)引導(dǎo)時(shí)間狀語從句的連接詞除上述外還有:
　�、賢ill, not … until …, until, before, since
　　Don't get off the bus until it has stopped.
　　He waited for his father until(till)it was twelve o'clock.
　　It will be five years before he returns from England