狀語從句可以用來表示條件、目的、時間、讓步、地點、原因、結果、行為方式和比較。
一、 表示條件的狀語從句可以由if, unless, in case, so(as) long as, so far as, on condition that,provided (that)等詞引導。
【點撥】? 1. 在if引導的條件狀語從句中,主句中的動詞常用一般將來時,從句中的動詞用一般現在時。如:If you ask him, hell help you.如你請他 (幫忙),他會幫你的。
2. 在if引導的條件狀語從句中,主句也可含有情態動詞或是祈使句。如:If it is fine tomorrow, we can go and fly the kite.如果明天天氣好,我們可以去放風箏。Dont miss the program if you like music.如果你喜歡音樂,不要錯過這個節目。
3. if除了可以引導條件狀語從句外,還可引導賓語從句,這時if = whether意為“是否”。如:I want to know if(=whether) he is our new teacher.我想知道他是不是我們的新老師。
4. unless意思是“除非,如果不”,相當于if...not。在unless引導的條件狀語從句中,主句中的動詞常用一般將來時,從句中的動詞用一般現在時。如:Unless it rains, the game will be played.=If it doesnt rain, the game will be played.除非下雨,否則比賽將照常進行。
5. 同if引導的條件狀語從句一樣,在unless引導的條件狀語從句中,主句也可以含有情態動詞或是祈使句。如:He cant see clearly unless he wears glasses.他不戴眼鏡就看不清楚。Dont touch the machine unless the teacher allows you to.沒有老師的允許,不要亂動機器。
【高考鏈接】? 1. Tom is so independent that he never asks his parents opinion__________ he wants their support.? ?(2019天津卷13)
A. since? B. once
C. unless? D. after
2.__________ you can sleep well, you will lose the ability to focus, plan and stay motivated after one or two nights.? ?(2018江蘇卷29)
A. Once? B. Unless
C. If? D. When
3.__________ we dont stop climate change, many animals and plants in the world will be gone.? ?(2018北京卷2)
A. Although? B. While
C. If? D. Until
4. You wont find paper cutting difficult__________ you keep practicing it.? ?(2015北京卷28)
A. even if? B. as long as
C. as if? D. ever since
5. It is so cold that you cant go outside__________ fully covered in thick clothes.? ?(2015江蘇卷26)
A. if? B. unless
C. once? D. when
二、 表示目的的狀語從句可以由that, so that, in order that, lest, in case, for fear that等詞引導。
【點撥】? 1. 目的狀語從句中一般含有情態動詞。如: Lets take the front seats that(=so that=in order that) we may see more clearly.我們坐前排吧,這樣我們看得清楚一些。
2. in order that可位于句首,而so或者so that則不可以。如:In order that he shouldnt wake up his wife, he left the room quietly.為了不吵醒妻子,他悄悄地離開了房間。
3. lest, in case, for fear that常用來表示“以免,以防”等意思,從句中的動詞形式多為should+動詞原形。在這一類從句中,should一般是不能省略的,但在lest, for fear that引導的從句中should有時可以省略。如:I wont make any noise, lest(= in case= for fear that) I should disturb you.我不會制造任何噪音,以免打擾你。
4. 在in case從句中,可以不用虛擬語氣而用陳述語氣,表示可能性較大。……