Why must an organism have the same amount of adenine as thymine

The upper forelimbs of humans and bats have fairly similar skeletal structures, whereas the correspondingbones in whales have very different shapes and proportions. however, genetic data suggest that all three kindsof organisms diverged from a common ancestor at about the same time. which of the following is the mostlikely explanation for these data? a) humans and bats evolved by natural selection, and whales evolved by lamarckian mechanisms.b) forelimb evolution was adaptive in people and bats, but not in whales.c) natural selection in an aquatic environment resulted in significant changes to whale forelimb anatomy.d) genes mutate faster in whales than in humans or bats.e) whales are not properly classified as mammals.