Correct answer: Nc41...K:d6 2.R:d7# 1.R:c5+?? 1...K:d6 2.R:d7# but 1...R:c5+! 1.N:c3+?? 1...K:d6 2.R:d7# but 1...K:d4! 1.Nc4! (2.R:c5#)
