Though both RNA and DNA contain the nitrogenous bases adenine, guanine and cytosine, RNA contains the nitrogenous base uracil instead of thymine. Uracil pairs with adenine in RNA, just as thymine pairs with adenine in DNA.
Answer is thymine because is DNA adenine pairs with thymine and cytosine always pairs with guanine, in RNA the only thing changed is that adenine pairs with Uracil
