連詞主要有：when as while before after until as soon as since等

(1)區(qū)別when, as, while的用法

①.when"當(dāng)......時(shí)候"引導(dǎo)的時(shí)間狀語從句，其動(dòng)詞既可以是延續(xù)性動(dòng)作的動(dòng)詞，也可以是瞬間性動(dòng)作的動(dòng)詞,如：

_________ the students heard the teacher's footsteps, they all stopped talking.

當(dāng)學(xué)生們聽到老師的腳步聲時(shí)，他們都停止了講話。(從句動(dòng)作發(fā)生在前)

② as"當(dāng).......時(shí)候"或"一邊.......一邊"引導(dǎo)的時(shí)間狀語從句其動(dòng)詞的動(dòng)作是延續(xù)性的，而且側(cè)重表示主句和從句的動(dòng)作并相發(fā)生：

We were having breakfast __________ she was combing her hair.

她梳頭時(shí)我們?cè)诔栽顼垺?/p>

③ while表示"在某一段時(shí)間里"或"在……期間"，其所引導(dǎo)的從句的動(dòng)作是延續(xù)性的，并側(cè)重表示和主句的動(dòng)作同時(shí)發(fā)生。如：

I can learn ________ I work.

我可以邊工作邊學(xué)習(xí)。

用when, as, while填空：

________ you came in, I was talking with a few boys.

It started to rain __________ we were playing outdoors.

They talked _________ they walked down the river.

__________ it was raining, the students were playing basketball.

Her brother watched TV__________ he ate supper.

(2) before引導(dǎo)的時(shí)間狀語從句，指時(shí)間上的"在……之前"

I'll be back _______________________________________________.

你離開之前我就會(huì)回來。

(3) as soon as表示"一……就"，做題要注意主將從現(xiàn)

As soon as we __________ (get) there, he ___________ (tell) us the news.

我們一到那，他就會(huì)告訴我們那個(gè)消息。

(4) since引導(dǎo)的時(shí)間狀語從句，從句的謂語動(dòng)詞通常為一般過去時(shí)，主句的謂語動(dòng)詞通常為現(xiàn)在完成時(shí)

We __________ never __________ (meet) since we ___________ (graduate) from the college.

大學(xué)畢業(yè)后我們就再?zèng)]見過面。

(5) till/until引導(dǎo)的時(shí)間狀語從句 till和until同義，作"直到……時(shí)(為止)"解，till多用于非正式文體，until多用于句首;not … until通常與after進(jìn)行轉(zhuǎn)換。如：

I won't go with you until(till) I finished my homework.

=____________________________________________________________________.

等我做完作業(yè)我才和你一起去。

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