A Proficient Engineer Can Easily Design Skeletal Structures That Are

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. That the actual forelimbs of these mammals do not seem to be optimally arranged is because

A) natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough 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 functions excellent, 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 generations and in previous species.