Please help, quickly!

This chart shows the beak length of a population of finches in the Galapagos. The island was faced with conditions causing the beak-length distribution in the population as shown in the graph. If natural selection occurs, how would you predict the bird beak lengths to change?
A. Only those with shorter beaks would survive.
B. The population would not really change much.
C. Only those with the longest beaks would survive.
D. Those with medium-long beaks would increase most.