1. Qe2 ... this move is tricky, yet devistating. Lets take a look at the issues it creates. It immediately threatens to checkmate on the next move (Qg2#) so white must stop this threat first. Unfortunately, there is only one option left for whitel to stop the checkmate (Rf2). Unfortunately, that move creates a forced checkmate for white once white follows with Qg4+, can you see the rest? This is a trickier problem. The only other option for white in this position would be to move their knight so that the queen could be used to stop the checkmate ... this of course drops the queen and prolongs the game.
2. a3 ... Some would debate that Rxh4 might be good here too. Many players will become worried about protecting their Rook on c4 since it is under attack; however, if black plays a3 right now and gives up the rook, then the pawn can not be stopped and black will get a queen for the rook.
3. c7 ... This move has some of the same logic as the previous puzzle (#2). There is no need to worry about the bishop on a6 since if black chooses to take it, the next move c8=Q+ wins the rook. The c7 move is strongest since it passes the pawn and most likely will win the rook anyways.