Probably missing something, but can't black escape mate by avoiding taking the Queen?
In which case I don't understand why Nd5+ isn't as good a move as the answer given. Is there a missing piece in the puzzle that would have prevented Nd5? Or am I missing an escape for black after 2. Nxe7?
In a real game I would decide for the fork.
If black plays 1. Ka5,Kb5 or Kc4 After we play 1.Qa3+, Black will lose the queen immediately.
the knight fork is just as good but not as pretty, i suggest the black queen be put on f8 rather than e7
But i suggest the white queen to be put on c1 instead of b2