Which Three Factors Were Necessary for Natural Selection to Occur

Which three factors were necessary for natural selection to occur among the finches on Daphne Major in the Grants' study?

A) The birds reproduced easily, the climate was constant, and the study went on for a long time.
B) The bird beak lengths varied, beak length was a heritable trait, and the drought limited the food supply so there was competition for food.
C) The bigger beaked birds survived the drought better, small beaked birds could produce big beaked offspring, there was plenty of food available.
D) There was a drought that limited food, the birds were adaptable, the study went on for a long time.
E) Finches reproduce quickly, finches can eat any kind of seed, the climate stayed mostly constant.