掌握： 1. when / while / as 2. before / after 3. till / until 4. since 5. as soon as, immediately, directly, instantly, the moment, the instant, the minute,
(3) 若主从句表示的两个同时进行的动作含有“一边…一 边”之意思，通常用 as： She sang as she went along. (4) 若从句是一个短暂性动作，主句是一个持续性动作， 可用 as / when 但不用 while： It was raining hard when [as] we arrived. (5) 若主从句表示的是两个同时(或几乎同时)发生的短暂 性动作，用 as / when： I thought of it just when [as] you opened your mouth. 就在你要说的时候，我也想到了。
注意： ①当使用连接词when表示“…时候”时，它所引导的 从句中谓语动词用一般现在时或者一般过去时，不能用 完成时态； ②when，while和as都引导表示时间的状语从句，它们 的区别在于动作发生的时间顺序。用when时，从句的 动作可以与主句的同时发生或先于主句动作发生；用as 时从句和主句动作同时发生；用while时从句和主句动 作同时发生，也可表示持续一段时间。
在复合句中由从句表示的状语称作状语从句，它 可以用来修饰谓语（包括非谓语动词）、定语或 状语，或是整个句子。
考核要求
准确掌握每一个连词的含义是掌握状语 从句的关键。
同时要注意主从句的时态呼应。
ቤተ መጻሕፍቲ ባይዱ
时间状语从句 地点状语从句 原 因状语从句 目的状语从句 结果 状语从句 条件状语从句 方式状 语从句 比较状语从句 让步状语 从句
Where, wherever, everywhere, anywhere
原因状语从句 because, as, since, seeing (that), now (that)
结果状语从句 so that, so…that, such…that
条件状语从句 目的状语从句
if，unless，as long as, suppose，supposing，in case，so far as， provided
(6) 若要表示两个正在发展变化的情况，“随着”，用 as： Things are getting better and better as time goes on. As it grew darker, it became colder. (7) when 可用作并列连词，表示“这时(突然)”； while 也可以用作并列连词，表示“而”、“却”(表 示对比)；但 as 则没有类似用法： We were about to start when it began to rain. He likes coffee, while she likes tea.
so，so that，in order that，for fear that，lest
让步状语从句 although, though, however (=no matter how), even if, whether…or 方式状语从句 as，as if，as though 比较状语从句 as…as，not as … as，than
状语从句类型
从属连词
时间状语从句 地点状语从句
when，whenever，while，as，before，after，since，now that， until，once，the moment，immediately，no sooner…than，the second，instantly， hardly
三者可表示“当…时候”，区别如下： (1) 若主句表示的是一个短暂性动作，从句表示的是一个 持续性动作，三者都可用：
He fell asleep when [while, as] he was reading. (2) 若主、从句表示两个同时进行的持续性动作，且强调 主句表示的动作延续到从句所指的整个时间，通常要用 while： Don’t talk while you’re eating. I kept silent while he was writing.
Before在…之前；After在…之后 表示主从句的动作先后发生 1.当主句用将来时，从句总是用现在时； 2.如果before引导的从句谓语用的是过去时，则主句动 词多用过去完成时； 3.After表示主句动作发生在从句动作之后。主句和从 句的动作的时间关系正好与before引导的从句相反。
1. It will be four days before they come back. 2. My father had left for Canada just before the letter arrived. 3. After you think it over, please let me know what you decide. 4. After we had finished the work, we went home
用when, while或as 填空:
1. _W__h_i_le_/__A_s_/__W_h__e_n__ we were talking, Mr. Smiths came in.
2. _W__h_e_n__ they came home, I was cooking dinner. 3. I was about to go to bed __w_h_e_n__ I heard
someone knock at the door. 4. __W_h_i_le___ we were watching TV, he was studying. 5. He is fat __w_h_i_le__ his brother is thin. 6. __A__s__ she sang, tears ran down her face.