More and more people have realized that how serious this problem is.

题目

More and more people have realized that how serious this problem is.
这个句子中that为什么要删掉?

答案

More and more people（主语） have realized （谓语）how serious this problem is（宾语从句）.
从句的引导词是关系副词how,已经有了.所以不能再有引导词that了.