What Processes Have Been Hypothesized to Influence the Evolution of Mutation

Multiple Choice

What processes have been hypothesized to influence the evolution of mutation rates?

A) natural selection only
B) genetic drift only
C) both natural selection and genetic drift, acting in the same direction to either increase or decrease mutation rates
D) both natural selection and genetic drift, acting in opposing directions: one process favors increasing mutation rates and the other favors decreasing mutation rates