Which of the Following Statements About the Movement of Materials

Which of the following statements about the movement of materials in a nerve axon is TRUE?

A) Movement along microtubules in the axon is slower than free diffusion, but necessary due to the importance of directional transport.
B) The small jerky steps seen when vesicles move along microtubules are due to the shrinkage of microtubules that occurs when axonal microtubules undergo dynamic instability.
C) Microtubules within an axon are arranged such that all microtubules point in the same direction with their minus ends toward the nerve cell body.
D) Microtubules within the axon support the unidirectional motion of materials from the nerve cell body to the axon terminal, while materials transported back from the axon terminal to the cell body move along intermediate filaments.