Answer:
A. reflects the genetic variation of a population.
Step-by-step explanation:
"Genetic variation" refers to the diversity of organisms' DNA. This also refers to the differences among the genes in a population.
"Genetic trait" refers to the characteristics possessed by an individual according to his DNA. This can be transferred from the parent to the off spring.
In order to know whether a sample is large enough, it is important to consider whether it reflects the genetic variation of the population. This will allow diversity of the organisms, thereby involving many characteristics, which is important in the study.
So, this explains the answer.