Rosemary and Peter Grant of Princeton University have studied finches on the Galapagos Islands since 1973. They found that when drought conditions on the islands increased, the seeds produced by some of the plants that provided food for the finches were affected. The drought decreased the supply of plants that produced easily cracked seeds, but permitted the survival of plants that produced larger, tougher seeds. Only finches with strong, wide beaks could break open the tougher seeds. What can you conclude about the effect of drought on the natural selection of beak size and shape in finches from the Galapagos?

A
Over time drought caused average numbers of finches with stronger, wider beaks to increase.
B
When average rainfall decreased, the number of finches that consumed easily cracked seeds went up.
C
When average rainfall increased, the number of finches that consumed easily cracked seeds went down.
D
Drought caused average seed size and shape to decrease, which caused number of finches with stronger, wider beaks to increase.