Tactics Trainer #0025392 problem
Qc7 and Qb8 don't work because the white knight gets around to those squarse, 3. ... Qc7 4. Nfd3 Ba6 5. Nxb4! and now the knight is threatening to take on a6 which attacks the c7 queen.
Black could play 3. ... Qc7 4. Nfd3 Qc3 and probably have an edge with the bishop pair and an advanced passed pawn. But Black can be up a whole piece, so I think Qc7 is really inferior to winning the piece.
The point was that at move 3 it's not a very nice problem, since only one of the three winning moves is credited as correct.
Tactics trainer problem #0025392 has a problem. There are 3 equally winning moves on move 3, only one of them is credited as correct.