what is a noun clause?
Noun clauses perform the same functions in sentences that nouns do:
A noun clause can be a subject of a verb:
What Billy did shocked his friends.
A noun clause can be an object of a verb:
Billy’s friends didn’t know that he couldn’t swim.
A noun clause can be a subject complement:
Billy’s mistake was that he refused to take lessons.
A noun clause can be an object of a preposition:
Mary is not responsible for what Billy did.
A noun clause (but not a noun) can be an adjective complement:
Everybody is sad that Billy drowned. ............ cheers