Proteins are transported via axoplasmic transport at slow rates (0.5 to 2 mm per day) and fast rates (200 to 400 mm per day). The difference in transport rate directly results from:
a. the difference in the time spent per day in transport by kinesin on microtubules.
b. the site where the protein is synthesized
c. the substrate molecule used by the motor protein
d. the motor protein used to transport the proteins