This change alters the center of gravity and posture of the body because the uterus expands and shifts higher as the fetus grows during pregnancy.

This causes an increased strain on the muscles and ligaments supporting the vertebral column and leads to lower back pain.

Choice A is wrong because increased joint laxity does not alter the center of gravity and posture of the body.

It is caused by hormonal changes that loosen the ligaments throughout the body, resulting in decreased stability of the joints.

Choice C is wrong because increased muscle strain does not alter the center of gravity and posture of the body.

It is a consequence of the shift in the center of gravity and the weight gain during pregnancy, which put more pressure on the back muscles.

Choice D is wrong because decreased muscle strength does not alter the center of gravity and posture of the body.

It is not a common musculoskeletal change during pregnancy, although some women may experience fatigue or weakness due to hormonal changes or anemia.