The correct answer is: C) shortening of microtubules
Chromosome movement is possible thanks to changes in microtubule length. Several types of microtubules are involved. First, during the anaphase kinetochore microtubules shorten and consequently the chromosomes move toward the spindle poles. Then the astral microtubules that are anchored to the cell membrane pull the poles further apart. At the end of anaphase, the interpolar microtubules slide past each other and that additionaly separate the chromosomes.
