The human body is in the most stable equilibrium when

a. sitting because the center of gravity in the largest body mass is midway to the ground and the base of support is balanced between the two sides.
b. standing because the center of gravity in each body part is closest midline and the base of support is under the major body masses.
c. side-lying because the center of gravity in each body mass is closer to the ground and the base of support is broader.
d. lying supine because the center of gravity in each body part is closest to the ground and the base of support is broadest.

d