What will white (Manifold) play in move 39?

The game so far: 1. e4 e5 2. Bc4 Nf6 3. Nc3 Nc6 4. Nf3 Nxe4 5. Nxe4 d5 6. Bd3 dxe4 7. Rg1 Bf5 8. Bb5 exf3 9. Bxc6+ bxc6 10. Qxf3 Qd7 11. Qc3 f6 12. g4 Bxg4 13. Rxg4 h5 14. Re4 Qd5 15. Qf3 Rd8 16. d3 a6 17. b3 Qc5 18. Kd1 a5 19. Bb2 g6 20. Qxf6 Kd7 21. Rxe5 Qd6 22. Qxh8 Be7 23. Qg7 Rf8 24. Rxe7+ Qxe7 25. Qxe7+ Kxe7 26. Ba3+ Kf7 27. Bxf8 Kxf828. Kd2 Kf7 29. Re1 Kg7 30. Re7+ Kf6 31. Rxc7 h4 32. a4 g5 33. b4 Ke6 34. bxa5 Kd6 35. Rb7 Ke6 36. a6 Kd5 37. h3 Kc5 38. a7 g4

For each response, the average probability in the last four hours before close is measured. With 75% probability, two moves will be randomly drawn, with weight proportional to those market probabilities. With 25% probabilities, three moves will be randomly drawn in the same way. Then for each of the two or three candidate moves, a conditional market is created. The average probability in the last 4 hour of the conditional markets will be measured. The move with higher average probability will be chosen. 

https://manifold.markets/harfe/will-white-win-in-manifold-plays-ch

Any resign moves or draw offeers are not allowed in this move!

Invalid moves or duplicate moves will be removed from consideration.