A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because .

A) natural selection has not had sufficient time to create the optimal design in each case, but will do so givenenough time.
B) natural selection operates in ways that are beyond the capability of the human mind to comprehend.
C) in many cases, phenotype is not merely determined by genotype, but by the environment as well.
D) though we may not consider the fit between the current skeletal arrangements and their functionsexcellent, we should not doubt that natural selection ultimately produces the best design.
E) natural selection is generally limited to modifying structures that were present in previous generationsand in previous species.