中考英語(yǔ)知識(shí)點(diǎn)：when, while和as的區(qū)別

　　when引導(dǎo)的從句的謂語(yǔ)動(dòng)詞可以是延續(xù)性的動(dòng)詞，又可以是瞬時(shí)動(dòng)詞。并且when有時(shí)表示"就在那時(shí)"。

　　When she came in, I was eating.她進(jìn)來(lái)時(shí)，我在吃飯。(瞬時(shí)動(dòng)詞)

　　When I lived in the countryside, I used to carry some water for him.當(dāng)?shù)淖≡谵r(nóng)村時(shí)，我常常為他擔(dān)水。(延續(xù)性的動(dòng)詞)

　　We were about to leave when he came in.我們就要離開(kāi)，就在那時(shí)他進(jìn)來(lái)了。

　　While引導(dǎo)的從句的謂語(yǔ)動(dòng)作必須是延續(xù)性的，并強(qiáng)調(diào)主句和從句的動(dòng)作同時(shí)發(fā)生(或者相對(duì)應(yīng))。并且while有時(shí)還可以表示對(duì)比。例如:

　　While my wife was reading the newspaper, I was watching TV. (was reading是延續(xù)性的動(dòng)詞，was reading和was watching同時(shí)發(fā)生)

　　I like playing football while you like playing basketball.我喜歡踢足球，而你喜歡打籃球。(對(duì)比)

　　As表示"一邊…一邊"，as引導(dǎo)的動(dòng)作是延續(xù)性的動(dòng)作，一般用于主句和從句動(dòng)作同時(shí)發(fā)生;as也可以強(qiáng)調(diào)"一先一后。

　　We always sing as we walk.我們總是邊走邊唱。(as表示"一邊…一邊")

　　As we was going out, it began to snow.當(dāng)我們出門(mén)時(shí)，開(kāi)始下雪了。(as強(qiáng)調(diào)句中兩個(gè)動(dòng)作緊接著先后發(fā)生，而不強(qiáng)調(diào)開(kāi)始下雪的特定時(shí)間)

　　有時(shí)這三個(gè)連詞可以互換，有時(shí)不可以。

　　lt was raining hard when (as) I got there.

　　我到那里時(shí)，正在下大雨。 ( 動(dòng)作同時(shí)發(fā)生，when可換為as, 但不能換為while，因?yàn)間et是點(diǎn)動(dòng)詞.)

　　When I had read the article, he called me.

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