Okay, let's try this.
Would it be a valid vote if I just say C?
Cause as I take it, it's C1 and C2 and not C and D because you would first see which of A, B or C gets most votes, for which you count C1 and C2 togehter, then if C wins, you compare number of C1 and C2 votes. This way I can just vote C so that it counts on the first round and doesn't matter on the second. Do I get it right?