Answer:
The correct option is A.
Step-by-step explanation:
In the field of ecology, directional selection can be described as a type of natural selection in which a single phenotype is abundant and favoured by natural systems, instead of the other phenotypes. As a result, phenotype frequency of the population tends to change.
The graph, A, shown the phenomenon of directional selection and the graph illustrates a single phenotype being favoured in it.