課本中不會教你的[W]714　when，while，after，before，if+分詞等

714　when，while，after，before，if+分詞等

① when，while引導(dǎo)狀語從句時，如果從句的主語同主句的主語為同一人或物，從句中的主語及助動詞be常可省略，采用“從屬連詞+現(xiàn)在分詞、過去分詞或介詞短語等”結(jié)構(gòu)。

He met an old friend when walking along the road. 在路上走著時，他遇見了一位老朋友。（=When he was walking along the road）

Be careful when crossing the road. 過馬路時要當(dāng)心。

When reading the letter，she couldn't help crying. 閱讀這封信時，她不禁哭了起來。（=When she was reading the letter）

While talking in the room，they heard a strange sound outside. 在房間里說話時，他們聽見外面有一個奇怪的聲音。（=While they were talking in the room）

While doing so，he decided to buy a car. 他做這事時決定買一輛車。（=While he was doing so）

When in trouble，ask her for help. 遇到麻煩時就請她幫忙。（=When you are in trouble）

While in London he studied English very hard. 他在倫敦時努力學(xué)習(xí)英語。（=While he was in London）

② after和before引導(dǎo)時間狀語從句時，如果從句的主語同主句的主語為同一人或物，常可轉(zhuǎn)換為“after、 before+現(xiàn)在分詞”結(jié)構(gòu)。

After going over the lessons，she went to bed. 她復(fù)習(xí)完功課后就睡了。（=After she went over the lessons）

After having worked for a whole day，he felt a bit tired. 工作了一整天之后，他感到有點累。

Before moving to Shanghai，she had lived in Hangzhou for twenty years. 在搬到上海之前，她已在杭州住了20年。（=Before she moved to Shanghai）

Before beginning to do his homework，he had watched TV half an hour. 在開始做作業(yè)之前，他已看了半個小時的電視。（=Before he began to do his homework）

③ if引導(dǎo)的從句如果是被動語態(tài)，而且從句的主語同主句的主語又相一致時，從句中的主語和be動詞可省略，轉(zhuǎn)換為“if+過去分詞”結(jié)構(gòu)。

If given more time，I could do the work better. 如果給更多時間的話，這項工作我可以做得更好。

If given another chance，he may succeed. 如果再給一次機(jī)會的話，他可能會成功的。