Injections of L-Dopa, the Precursor of Norepinephrine, Can Enable Spinally

Injections of L-dopa, the precursor of norepinephrine, can enable spinally transected cats to walk on a treadmill. The most likely explanation for this result is that

A) norepinephrine stimulates spinal motor neurons, causing muscle contractions.
B) norepinephrine acts on the neuromuscular junctions of the limb muscles and causes muscle contractions.
C) norepinephrine activates sensory afferents that cause reflex muscle contractions in the limbs.
D) norepinephrine activates the central pattern generator that causes rhythmic stepping motions.