Because for the strands to form a double helix the base pairs have to match perfectly (adenine with thymine and cytosine with guanine) in DNA , and if a strand of RNA is paired with a split strand of DNA it goes adenine with uracil and cytosine with guanine (uracil replaces thymine)
The answer is A, the other answer choices are bad for the environment
Water temperature i believe i think i had that test but try water temperature