Answer:
D: an animal moves to a new population and mates
Explanation:
Gene flow, also known as gene migration, is the transfer of genetic material (DNA) from the population of a species to another population of the same species. Gene flow can be caused by migration of one member of a particular population that interbreeds in another population or due to aided transfer of gametes from one population to another, as in the case of cross-pollination.
Based on the above definition, an animal moving from its own population to a new population and mates there represents a scenario that causes gene flow.
In the first option, one flower of a population is pollinating another flower in the same population. This doesn't show gene flow because there is no transfer of genes (present in gametes) to a different population.
