Can CPCTC be used twice in a proof?

Yes, CPCTC (Corresponding Parts of Congruent Triangles are Congruent) can be used multiple times in a proof, provided that you have established the congruence of the triangles involved. Each instance of CPCTC can be applied to demonstrate the congruence of different corresponding parts as needed throughout the proof. Just ensure that the triangles being referenced are congruent before applying CPCTC.