Plz, help me! when a population splits into two subgroups, what is the likely to cause the subgroups to develop different traits

a. the occurrence of natural selection in both subgroups at the same time
b. the occurrence of the divergence in one subgroup but not the other
c. the occurrence in one subgroup of mutations that are not passed to the other through reproduction
d. an increase in gene flow in the two subgroups that are formed