Jim is agood-at-maths boy
这已经是个完整的句子了 不用加 be
good-at-maths 几个词连起来构成 形容词
He is a two years old boy
He is a two-year-old boy
或者用 定语从句
Jim is a boy who is good at mathes
望采纳!祝学习进步!你发的很好，我是个六年级的男孩，谢谢你解决我的语法问题，如果今天没人比你更好，我会采纳你！Thank you very much.呵呵能回答我第三个问题吗？谢谢诶第三个问题已经回答你了定语从句Jim is a boy (who is good at mathes)限制定语从句你们还没学到吧