问题描述：
they do not doing their homework为什么不对呀?
我看新概念上面说是 they are not ding their homework.
不是说BE动词后面不能跟动词吗?DO不是动词吗?
我看新概念上面说是 they are not ding their homework.
不是说BE动词后面不能跟动词吗?DO不是动词吗?
问题解答：
我来补答展开全文阅读