Help me understand why Nelson (bot) won't take a bishop/knight

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TheAmazingIdiot
I'm black in this game, I used a hint and it said to put my bishop on D3 (can someone explain why as it's free whilst still protecting the rook, no?) I don't get the idea of this move but more perplexing is that the bot refuses to take it even though it's a free piece. I've tried redoing the move for different results but he won't take it. . e4 d5 2. Qh5 c6 3. e5 g6 4. Qe2 Bf5 5. b3 e6 6. Bb2 Bxc2 7. Na3 Bf5 8. Qd1 Nd7 9. Nc4 dxc4 10. Bxc4 Ne7 11. Qf3 Nc5 12. d4 Ne4 13. Rb1 Qa5+ 14. Ke2 Qd2+ 15. Kf1 Qc2 16. Rd1 Bg4 17. Bd3 *
justbefair
TheAmazingIdiot wrote:
I'm black in this game, I used a hint and it said to put my bishop on D3 (can someone explain why as it's free whilst still protecting the rook, no?) I don't get the idea of this move but more perplexing is that the bot refuses to take it even though it's a free piece. I've tried redoing the move for different results but he won't take it. . e4 d5 2. Qh5 c6 3. e5 g6 4. Qe2 Bf5 5. b3 e6 6. Bb2 Bxc2 7. Na3 Bf5 8. Qd1 Nd7 9. Nc4 dxc4 10. Bxc4 Ne7 11. Qf3 Nc5 12. d4 Ne4 13. Rb1 Qa5+ 14. Ke2 Qd2+ 15. Kf1 Qc2 16. Rd1 Bg4 17. Bd3 *
You said you were black. I don't understand when black would put a bishop on d3. I think you must have been white.
 
If you were white, the move makes some sense because, even though your queen on f3 remains hanging, the move Bd3 tries to put you in a position to take the black knight on e4, which black had been threatening to use with its queen in a checkmate on f2. 
 
(The white queen can't take the bishop on g4 because then white would get mated by the black queen on f2.)