Bipedal behavior and a skeleton adapted for bipedalism were not weeded out by natural selection ...

Bipedal behavior and a skeleton adapted for
  bipedalism were not weeded out by natural selection
  because they
  a. improved stability during locomotion.
  b. enabled the forelimbs to efficiently manipulate
  the environment.
  c. accelerated the development of binocular vision.
  d. improved stability during locomotion and
  enabled the forelimbs to efficiently manipulate
  the environment.
  e. improved stability during locomotion, enabled
  the forelimbs to efficiently manipulate the
  environment, and accelerated the development
  of binocular vision.

Question 2

The conclusion that early hominids were bipedal is
  based in part on examination of
  a. their S-shaped backbone.
  b. the position of the foramen magnum.
  c. footprints.
  d. positions of the foramen magnum, S-shaped
  backbone and footprints.
  e. length of the femur.