狀語從句指句子用作狀語時，起副詞作用的句子。它可以修飾謂語、非謂語動詞、定語、狀語或整個句子。
　　根據(jù)其作用可分為時間、地點、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通常用逗號與主句隔開，位于句尾時可以不用逗號隔開。
　　讓步狀語從句
　　(1)although與though可以引導(dǎo)讓步狀語從句，不能與but連用，但可以與yet連用。
　　Although they are poor,(yet)they are warm-hearted.
　　(2)even if或even though引導(dǎo)讓步狀語從句，表示“即使”，"“縱然”，用來使人注意下文所強調(diào)內(nèi)容的性質(zhì)。
　　I'll get there even if(though)I have to sell my house to get enough money to go by air.
　　(3)no matter后接上who、what、where、how等疑問詞，也可以在這類疑問詞后面加上ever構(gòu)成whoever、whatever、wherever、however等。
　　Don't trust him, no matter what / whatever he says.
　　Whoever breaks the law will be published.
　　No matter how hard the work is, you'd better try to do it well.
　　(4)as也可以引導(dǎo)讓步狀語從句，要用倒裝。
　　Child as(though)he is, he knows a lot.
　　Much as I like it, I won't buy.
　　Try as he would, he couldn't lift the heavy box.
　　時間狀語從句
　　(1)as、when、while
　　as表示“當(dāng)……的時候”，往往和when/while通用，但它著重強調(diào)主句與從句的動作或事情同時或幾乎同時發(fā)生。
　　She came up as I was cooking.(同時)
　　The runners started as the gun went off.(幾乎同時)
　　when：(at or during the time that)既可以表示在某一點的時候，又可表示在某一段時間內(nèi)，主句與從句的動作或事情可以同時發(fā)生也可以先后發(fā)生。
　　It was raining when we arrived.(指時間點)
　　When we were at school, we went to the library every day.(在一段時間內(nèi))
　　while意思是“當(dāng)……的時候”或“在某一段時間里”。主句中的動作或事情在從句中的動作或事情的進展過程中發(fā)生，從句中的動詞一般要用延續(xù)性動詞。在when表示a period of time時，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.