Answer:
a. Low genetic diversity
Explanation:
Natural selection is the process of differential survival and reproductive rates among the individuals of a population. Natural selection works on the existing genetic diversity of the population and favors the genetic traits that impart survival advantage to the individuals.
In the absence of genetic diversity or low genetic diversity in a population would not allow the natural selection to increase the frequencies of the alleles responsible for adaptive genetic traits. This would pause the process of evolution carried out by natural selection.