Answer:
The most appropriate answer would be c. Is there a theory that explains the results in the graph?
The change in the frequency of the alleles in a population is a normal observation.
However, it is important to know the reason or theory behind that change.
For example, the reason may include natural selection, competition, genetic drift, mutation et cetera.
The theory or reason might help us to understand the effect of nature, mutation, genetic drift et cetera on the allele frequency