Correct answer: Kd21...Kh3 2.Bf1# 1...Kf3 2.O-O# 1.Nd4?? (2.Bf1#) but 1...Kh3! 1.Bf4?? zz 1...Kh3 2.Bf1# 1...Kf3 2.O-O# but 1...e3! 1.Bg5?? zz