Some Evolutionary Biologists Argue That, Overall, Regulatory Mutations Are More

Some evolutionary biologists argue that, overall, regulatory mutations are more likely to result in adaptation than changes in the protein-coding sequence of genes. Considering the logic underlying their argument, in which case below would this expectation not apply to a particular gene involved in adaptation?

A) The gene is involved in multiple functions.
B) The gene is involved in only one function.
C) The gene is expressed in different tissues.
D) The protein encoded by the gene performs an important function.