They always let me do what I think I should.必须用what

不可以用that
不是定语从句, 是宾语从句.因为在动词后.

该怎么区分:名词后的从句是定语从句;动词后的从句是宾语从句;

They always let me do what I think I should.宾语从句

They always let me do the work that I am not interested in.定语从句