The correct answer is 2. Head positioning is the stimulus for the symmetrical tonic neck reflex such that when the head is flexed, the upper extremities flexed in the lower extremities extend, and when the head extends, the upper extremities extend, and the lower extremities flex. Thus, if this reflex were not integrated, the extremities would not allow the infant to maintain a quadruped position.
The Galant reflex is stimulated by stroking lateral to the spine, with the correct response being lateral side bending to the same side as the side of the stimulus.
The plantar grasp reflex is stimulated by placing pressure on the ball of the foot, generally in standing, and the correct response is for the toes to curl or flex.
The positive support reflex is stimulated by bearing weight through the feet, and the correct response is for the lower extremities to extend, thereby allowing the infant to bear weight through the lower extremities.