Correct answer: Rbd71...Nc7 2.Rb6# 1.Rbb5?? zz 1...Nb4/Nb8/Nc5 2.Rbc5# 1...Nc7 2.Rb6#/Rbc5# but 1...Kc7! 1.Rdd7?? zz 1...Nb4/N