Kb6 (if 2...h3, then 3.Ke6 h2 4.c7 Kb7 5.Kd7 allows white to promote his pawn) 3. Ke5! Now, if 3...Kxc6, then 4.Kf4 stops Black's pawn after all, while if 3...h3 4.Kd6 allows White to promote his pawn.