Answer
C.
Work Step by Step
For two homologous genes to regulate different processes in different organisms, the expression pattern of that gene itself must be changed between the two homologs (C.). D. is wrong because Tbx5 is not a signal molecule, and A. is wrong since it is not part of bone. B. can be excluded since Tbx5 does bind to FGF-10, but it is not a transcription factor.