Fossilized Foot Bones Show That Some Hominids Living Between 3

Fossilized foot bones show that some hominids living between 3 and 3.5 mya walked upright but had partially opposable big toes.This suggests that

A) the shift to bipedalism was not sudden and complete, and the earliest bipedal hominins may have also spent some time in the trees for shelter or to find food.
B) the shift from quadrupedalism to bipedalism happened abruptly about 2.5 mya when hominins could no longer find any food in trees.
C) hominins actually shifted from bipedalism to quadrupedalism, as it proved to be an advantage when acquiring food.
D) having a partially opposable big toe helped bipedal hominins run faster to avoid their predators.