Which of the following statements about microtubules is FALSE?

a) The microtubules serve as tracks for motor proteins, which carry "cargo" to new cellular locations.
b) The microtubules are essential for distributing chromosomes to daughter cells during cell division.
c) Actin monomers can be rapidly added or subtracted from the end of the microtubule, thereby changing its length.
d) The microtubules form a rigid internal skeleton for some cells.
e) All of the above statements are correct. (Do not select this answer if one of the above choices is false.)