Final answer:
Gene flow tends to decrease divergence between populations by introducing new genetic variation and can limit local adaptation, making 'a and c correct' the right answer.
Step-by-step explanation:
When examining gene flow, it is referred to as the movement of alleles into or out of a population due to the migration of individuals or gametes. Gene flow has several implications for the evolution and diversity of populations. Primarily, it decreases divergence between populations by introducing new genetic variation, thereby homogenizing the gene pools of interconnected populations. On the other hand, restricted gene flow can lead to increased divergence and even speciation. Additionally, gene flow can limit adaptation in some populations if the incoming alleles counteract the effects of selection favoring local adaptations.
Therefore, the correct answers in the context you provided would be that gene flow A. decreases divergence between populations and C. can limit adaptation in some populations. Hence, D. 'a and c are correct' is the correct statement regarding gene flow.