The correct answer to this question is A. Centromeres are the region of a chromosome where the microtubules of the spindle attach during cell division. Centromeres are at the end of the chromatid where two replicated sister chromatids are attached.
Centromeres only appears when DNA replication occurs. The normal number of chromosomes in the cell is 10, and there are normally 5 chromosome pairs. With 20 chromatids, there would be 2 identical pairs (sister chromatids) after they have gone through replication. So there would be 10 centromeres, because you would divide the 20 chromatids in half to get the 10 centromeres.
Centromeres are the point at which two replicated sister chromatids are attached and only appear when DNA replication occurs. Meaning that the normal number of chromosomes in the cell should be 10 and there should normally be 5 chromosome pairs. Now that there are 20 chromatids they should be in identical pairs of 2 (sister chromatids) as they have undergone replication. Therefore there would be 10 centromeres.