职称英语理工类语法词汇常见考点：时间状语从句

　　状语从句在复合句中作状语，修饰主句中的谓语动词、副词、形容词或整个句子。根据句子的含义，它可表时间、地点、原因、目的、结果、条件、行为方式、比较、让步等。状语从句通常由一个连词引起，有时由一个起连词作用的词组引起。

　　一.时间状语从句

　　I) when，while和as

　　He entered the room when the meeting was going on.

　　when 通常指一时的动作或状态，可表示从句动作与主句动作同时发生，或先于主句动作;while常用来引导两个同时进行的持续时间较长的动作;as常用来引导两个动作紧接着发生，强调同一时间或一前一后。

　　When I meet the right chance, I will try my best.

　　While the teacher explained the text, the students listened attentively and took notes

　　He sang songs as he was taking a bath.

　　As spring warms the earth, all flowers begin to bloom.

　　注：when有时作并列连词意为正在这时、突然，在句末，不能位于句首。从句的谓语动词常用一般过去时，主句通常用过去进行时、过去完成时或be about to结构等。

　　She was about to leave when Mark arrived so she stayed a little longer.

　　He had been walking under the trees when an apple fell down.

　　Ⅱ) as soon as, hardly when , no sooner than 等引导的时间状语从句，意为 一 就

　　Jack had scarcely /hardly seen me when he left the room.

　　The spy had no sooner returned home than he was told to go to another country.

　　那个间谍一踏进国门就奉命要去他国。

　　注： 在no sooner than, hardly when 引导的时间状语从句中，若把no sooner, hardly, scarcely, barely 放在句首，则要用倒装结构。

　　No sooner had he heard the news than he fainted.

　　Scarcely had he entered the room when the telephone rang.