Answer:
c. disruptive selection
Step-by-step explanation:
Disruptive selection, which is also called diversifying selection, is a form of natural selection that causes individuals with intermediate trait to be less favored to survive and reproduce, while those with extreme traits are favored by the evolutionary forces, making them to survive and reproduce more.
Disruptive selection would act on shell color in the snails causing the alleles for the extreme traits to increase in frequency while that of intermediate values will decrease resulting in the population being divided mainly into two groups.