摘要：(二)情态动词在一般时否定句中的用法 can't 表示“不可能 . may not 表示“不可以 . mustn't 表示“一定不要 .“不许可 .needn't 表示“不必 .dare not +动词原形表示“不敢 . He can't finish his essay by this time. 现在他不可能写完论文. He may not sleep now. 他或许现在没在睡觉. You mustn't criticize her in that way. 你不应那样批评她. You needn't come tomorrow. 你明天没必要来了. He dared not meet his fiancée. 他不敢见女朋友. (三)can.may.must三者用法比较 can.may.must是三个最重要的情态动词.其基本句型如下: 肯定句:主语+can.may.must +动词原形 否定句:主语+can.may.must +not +动词原形 疑问句:Can.May.Must +主语+动词原形
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理解下在句子，翻译句中划线部分，并归纳其用法：
On no account you should attempt this exercise if you're seriously ill．(判断正误)________
1．It was not until yesterday that I met my old friend．
2．It is in a small factory that my brother is going to work．
It在1、2句中构成________句型。请用横线划出被强调的成分。