What Is the Most Important Difference Between Australopithecus Afarensis and the Modern

What is the most important difference between Australopithecus afarensis and the modern apes?

A) Australopithecus afarensis had increased cranial capacity.
B) Australopithecus afarensis had better color vision than apes.
C) Australopithecus afarensis had a narrow chest, whereas living apes have a barrel chest.
D) Australopithecus afarensis had lost its prehensile tail.
E) Australopithecus afarensis was bipedal.