When和While的區(qū)別
①when是at or during the time that,既指時間點,也可指一段時間,while是during the time that,只指一段時間,因此when引導的時間狀語從句中的動詞可以是終止性動詞,也可以是延續(xù)性動詞,而while從句中的動詞必須是延續(xù)性動詞.
②when 說明從句的動作和主句的動作可以是同時,也可以是先后發(fā)生；while 則強調主句的動作在從句動作的發(fā)生的過程中或主從句兩個動作同時發(fā)生.
③由when引導的時間狀語從句,主句用過去進行時,從句應用一般過去時；如果從句和主句的動作同時發(fā)生,兩句都用過去進行時的時候,多用while引導,如：
a.When the teacher came in,we were talking.
當此句改變主從句的位置時,則為：
While we were talking,the teacher came in.
b.They were singing while we were dancing.
④when和while 還可作并列連詞.when表示“在那時”；while表示“而,卻”,表對照關系.如：
a.The children were running to move the bag of rice when they heard the sound of a motor bike.
孩子們正要跑過去搬開那袋米,這時他們聽到了摩托車的聲音.
b.He is strong while his brother is weak.
他長得很結實,而他弟弟卻很瘦弱.