The correct option is D Australopithecus
The Lucy specimen is an early Australopithecus afarensis and is dated to about 3.2 million years ago. The skeleton presents a small skull similar to that of non-hominin apes, plus evidence of a walking gait that was bipedal and upright, similar to that of humans (and other hominins), this combination supports the view of human evolution that bipedalism preceded the increase in brain size.
Therefore, the correct answer is option D.