The answer is C, because RNA uses Cytosine (C), Guanine (G), Adenine (A), and Uracil (U), but you are looking for the DNA strand so instead of Uracil (U) you use Thymine (T), and furthermore you find the base DNA strand by finding the opposite of the letters using the base pair rule. The rule states in DNA C pairs with G, and A pairs with T, and in RNA A pairs with U.
