In the Experiments in Which the Cat's Mesencephalic Locomotor Region

In the experiments in which the cat's mesencephalic locomotor region was transected, strength of stepping was proportional to strength of electrical stimulation applied to this nucleus but had no effect on speed. What is a plausible way to centrally control stepping speed (running) ?

A) Stimulating the basal ganglia
B) Stimulating the deep cerebellar nuclei
C) Stimulating the motor cortex
D) Inhibiting the deep cerebellar nuclei
E) Inhibiting the basal ganglia