Are these noun clauses correct?
A. What you said.
B. What is important.
c. Who the principal of this school is.
D. What this is.
E. What is going on.

Then,are these sentences correct? I am using them as a subject.
a. What is important is that we need to hurry up.
b.what's going on is not important.
c. What you said was heart touching.

What's the difference ?
A. Where did you get a haircut and where did you have/get your hair cut.

Thank you.