Zwischenzug (solve this problem!)

We went over the Famous Checkmates worksheet.
Then we had a lesson on the tactic known as Zwischenzug, followed by a worksheet on that.
Here's a problem I put on the display board - find White's best move.

White would like to put some pressure on the black king. He can threaten checkmate with Qf3, Qf4 or Qh5. Which works best?
a) 1. Qf4 Re3 pretty much stops the threat
b) 1. Qh5 looks more powerful because you are also attacking Black's bishop, but Black plays Be7 saving the bishop and stopping checkmate.
c) 1. Qf3 is a fork threatening mate and the black queen, but black can trade queens (or so Black thinks!)  Qxf3. But White has a Zwischenzug move up his sleeve. He's going to take the queen, but not just yet. Can you find the move?

I dropped a few students who haven't been here in months.

Grade	Rank	Name	27-Feb
8	1	Owen	1081
7	2	Luke	980
7	3	Graham	599
5	4	Shanmuka	517
?	5	Elijah	419
5	6	Billy	400
?	7	Amanuel	354
6	8	Tyler	309
6	9	Zach	274
5	10	Carlos	242
5	11	Adrien	231
6	12	Justin	178
?	13	Bisrat	156
5	14	Manogna	154
6	15	Sahasra	148
?	16	Benny	132
5	17	David	116
?	18	Sam	100
?	19	Nahom	100