Answer:
C
Explanation:
The helix has to unwind before separating. Once it's separated, then new bases can be added. Once the bases are added, the separate strands wind into helices.
C. The number of covalent bonds is equal to the number of unpaired valence electrons. For example, nitrogen and phosphorous both have 3 unpaired valence electrons thus forming 3 covalent bonds.
Centromeres split apart during anaphase.
spindle fibers pull the to sister chromatids apart.