bob sings well .he can---in our school music festival

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bob sings well .he can---in our school music festival

bob sings well .he can-sing--in our school music festival
Bob唱得很好.他可以在我们学校音乐节上唱歌.bob sings well.he can---in our school music festival1.is 2.am 8.be4.areC.be can 后面必须使用动词原形为啥语法规定,情态动词后面必须跟动词原形。be不是动词be是系动词的原形