2017职称英语考试语法知识点英语职称考试：时间状语从句

　　时间状语从句

　　(1)as、when、while

　　as表示“当……英语职称考试的时候”英语职称考试，往往和when/while通用，但它着重强调主句与从句的动作或事情同时或几乎同时发生。

　　She came up as I was cooking.(同时)

　　The runners started as the gun went off.(几乎同时)

　　when：(at or during the time that)既可以表示在某一点的时候，又可表示在某一段时间内，主句与从句的动作或事情可以同时发生也可以先后发生。

　　It was raining when we arrived.(指时间点)

　　When we were at school, we went to the library every day.(在一段时间内)

　　while意思是“当……的时候”或“在某一段时间里”。主句中的动作或事情在从句中的动作或事情的进展过程中发生，从句中的动词一般要用延续性动词。在when表示a period of time时，两者可以互换。

　　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，这里的while意思是“趁……”)

　　(2)引导时间状语从句的连接词除上述外还有：

　　①till、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.

　　来源：新东方在线论坛