For Generations, Neighborhood Children Had Left Their Sexually Reproducing Multicolored

For generations, neighborhood children had left their sexually reproducing multicolored bean collection unprotected and scattered on the sidewalk after play. One day, bean-eating birds invaded their neighborhood looking for food. The next generation of beans all were mostly gray (sidewalk-colored) . What type of genetic evolution caused the generational shift?

A) ecological selection
B) sexual selection
C) artificial selection
D) gene flow
E) industrial melanism.