Answer: C. Large amount of inherited genetic variation.
If you had a population where the genetic variation wasn't as high or practically non-existent, then that population is likely suited to that very narrow specific environment. If the environment doesn't change, then the population wouldn't have a problem. However, the environment isn't likely to stay static. Things change all the time and this change will bring challenges to the population that was suited for the old environmental conditions.
Populations with high genetic variability will have some individuals thrive while some unfortunate members will perish. The members that die off are likely the ones who cannot adapt to the changes. As the environment changes, the individuals who survive will pass on their DNA to their offspring, allowing for natural selection to reinforce those favorable traits. Since the environment is constantly changing, whether that change is slow or fast, this means the process is continued indefinitely. So that's why high genetic variability is favored.