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

Ascientist is investigating the effects of salinity on fish development. he places fertilized fish eggs in an aquarium that contains low salinity and observes their development. what factor would improve experimental design the most? place the fish eggs in the open ocean because that is the natural habitat include another aquarium that has normal salinity to compare to the low salinity aquarium include an aquarium that replaces salt with sugar to confirm that the effects are specific to salt grow algae with the fish eggs in order to provide adequate nutrients to the developing embryos