they are some difficult math problems.改为单数句 ____ ____ difficult math problems.
问题描述：
they are some difficult math problems.改为单数句 ____ ____ difficult math problems.
答
首先你的拼写有误，最后一个词应该是单数的problem
It's a difficult math problems.
答
it is difficult math problem
答
There's a difficult math problem.