Which of the following is true of kinetochores?
a. The are the sites at which microtubules attach to chromosomes.
b. They cross at the cell's equator and move against each other, causing the cell to elongate.
c. They are the primary centrosome structures that maintain the attachment of the sister chromatids prior to mitosis.
d. They are located at the center of the centrosome and organize tubulin into spindle fibers.
e. They attach to the ring of actin along the cytoplasmic surface of the plasma membrane, causing the actin to contract to form the cleavage furrow.