Noun clauses.

https://docs.google.com/a/canada-english.com/document/d/18m-k51Ml6TXkcBct-CVhXyzAJHL3IOv5D-spJU0WQaU/edit?authkey=CKisuskG&hl=en_US

Yes / no question                  =	If / whether clauses
Questions (what, how etc)                                                                                                        =	Question word clauses
Statements                             =	That clause