it-cleft sentences

[paracompact]

1) Who was it that left the room last?
(from a grammar book for Japanese high school students)

2) What was it (that) the man was saying?
(my original sentence)

3) I caught on to what it was the guy was saying.
(catch on)

[QUESTION 1]
Is #1 an it-cleft sentence?

[QUESTION 2]
Is #2 an it-cleft sentence?

[QUESTION 3]
Is the underlined part in #3 an it-cleft construction?

[QUESTION 4]
Is the "what" in #3 a relative pronoun (meaning "the thing which") or an interrogative pronoun?

For the definition of "it-cleft sentence", please click here.

[Alan]

Q1-3: yes

Q4: a nominal relative pronoun (= that which)