A centromere is:
A. Composed of a ring of microtubules; they occur in pairs, making up the centrosome.
B. Composed of microtubules wrapped in an extension of the plasma membrane; they can bend, are important for propulsion, and may be found on the cell surface.
C. A microtubule-organizing region out of which microtubules grow; it's composed of a pair of centrioles.
D. The region of a duplicated chromosome where two sister chromatids are joined and where spindle microtubules attach during mitosis and meiosis.