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1、1.祈使句是表示命令、叮嘱、号召等的句子， 2.通常省略主语you. 3.句中谓语动词用动词原形。 4.祈使句有肯定和否定两种：,一、否定祈使句dont,肯定祈使句 Sit down, please. Come in, please. Eat lunch at home.,否定祈使句 Dont sit down. Dont come in. Dont eat lunch at home.,祈使句是用来表示请求、命令、叮嘱、号召或者劝告等的句子, 这类句子的主语常是第二人称you,也就是听话者,因而you常省去。祈使句的开头是动词原形。,Listen to music outside. Dont
2、 listen to music outside. Do your homework at school. Dont do your homework at school.,二、情态动词have to 的用法： 意思是“必须、不得不”,它侧重于客观上的必 和外界的权威 (1) 结构:主语have to动词原形其他 (一 般现在时,主语是第三人称单数时has to;句子是 过去时用had to)， 如：,We have to wear sneakers for gym class. Tom has to practice the guitar every day.,(2) 否定形式:主语dont
3、 have to动词原其 他 (一般现在时,主语是第三人称单数用doesnt have to; 句子是过去时用didnt have to), 如:,Nick doesnt have to wear a uniform. We didnt have to do our homework at once.,(3) 疑问句: Do (Does或Did) 主语have to 动词原形其他,如: Do you have to stay at home on weekends? Yes, I do. / No, I dont.,三、情态动词can的用法 表示能力 “会, 能”。,Can you play the guitar? Judy can speak a little Chinese.,(2) 表示允许、许可,意思是 “可以”“能”(在这一课中新学的词义)。,Can the students run in the hallways?,We can eat outside.,注意: 同样是情态动词, can 和have to 的用法 是有区别的, 和大部分情态动词一样, can在否 定句中, 直接在can后加上not, 在疑问句中, 把 can放到主语前面, 并且没有人称和数的变化。,
