Which of the following statements about DNA damage by ultraviolet (UV) light is true?

Which of the following statements about DNA damage by ultraviolet (UV) light is true?

A. The most common DNA damage due to UV light is the formation of dimers between adenine and guanine.

B. Dimers disrupt the shape of the double helix.

C. Thymine dimers form when cytosine is altered by UV light to form thymine, then linked covalently to an adjacent thymine.

D. Dimer formation is especially serious because they cannot be repaired by the normal repair enzymes in the cell.