In the study of finches' beaks, the biologists Peter and Rosemary Grant found that ________.
a. in only one generation, natural selection produced a better-adapted species
b. All of the choices are correct.
c. when heavy rains became common, birds with slender beaks flourished
d. Darwin had underestimated the power of natural selection
e. under drought conditions, more thick-than thin-beaked birds survived and reproduced