Unit 4 Don’t eat in class
单元语法专练
祈使句
1.定义。
用来表达命令、请求、劝告、警告、禁止等的句子叫作祈使句。祈使句通常省略主语you。例如:
Be quiet,please.请安静。
Please have a seat.请坐。
2.句式结构。
( 1 )Do型:动词原形+宾语+其他。例如:
Go this way,please.请这边走。
( 2 )Be型:Be+表语+其他。例如:
Be a good kid!做个好孩子!
( 3 )Let型:Let+宾语+动词原形+其他。例如:
Let me help you.让我来帮你。
注意:祈使句的否定形式一般是在动词原形前加don’t构成,有时也可直接用no开头表示禁止。例如:
Don’t be late for school!上学不要迟到!
No smoking!禁止吸烟!
have to与must的用法
have to和must均可表示“必须”。must更加强调说话者的主观意愿;而have to强调客观的必要性,意为“不得不”。两者的否定式含义大不相同。mustn’t表示“不准;禁止”,而don’t have to 表示“不必”。例如:
I must go now,or I’ll be late.我现在必须走了,不然我就会迟到了。
She has to help her mother look after her sister.她不得不帮着她妈妈照顾妹妹。
You mustn’t swim in the river.你不准在河里游泳。
You don’t have to do it now.你现在不必做这件事。
注意:以must开头的一般疑问句,其肯定回答用must,否定回答用needn’t或don’t have to。例如:
—Must I finish the work now?我现在必须完成这项工作吗?
—Yes,you must./No,you don’t have to.是的,你必须完成。/不,你不必现在完成。
Ⅰ.根据句意用所给词的适当形式填空
1. Do ( do ) the work right now,Jim.
2.Please tell ( tell ) me the news.
3.Let’s play ( play ) soccer now.
4.You must come ( come ) to school on time.
5.No talking ( talk ) here!
Ⅱ.根据句意用must或have to的适当形式填空
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1.You must do it yourself.
2.— Must I read the book in the reading room?
—No,you don’t have to .
3.It’s late.Jim has to go home.
4.— Must Lily keep quiet?
—Yes,she must .
5.You don’t have to get up early on weekends.
Ⅲ.按要求完成句子,每空一词
1.You can’t listen to music when your mother is sleeping.( 改为祈使句 )
Don’t listen to music when your mother is sleeping.
2.He has to be in bed by ten o’clock.( 改为一般疑问句 )
Does he have to be in bed by ten o’clock?
3.You must come here early this afternoon.( 改为祈使句 )
Come here early this afternoon.
4.Let her help you.( 改为否定句 )
Don’t let her help you.
5.She has to ride her bike to go home.( 改为否定句 )
She doesn’t have to ride her bike to go home.
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