be动词包含is,am,are/was,werebe是原形。有个顺口溜:我用am,你用are,is连着他,她,它; 单数名词用is,复数名词全用are。I won't be free this afternoon. I'll be seeing a friend off. won't是will的否定形式,而will是情态动词,规定:情态动词后要+动词原形,所以用be。情态动词有:can, must, should, would, may等。He is working.主语是he(他),所以be动词用is。
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