The correct option is C Uracil
There are two types of nitrogenous bases, namely purines and pyrimidines. Adenine and guanine are the purines while thymine, uracil, and cytosine are the pyrimidines. Adenine, guanine, and cytosine are common to both DNA and RNA. The thymine base of DNA is replaced with uracil in RNA. So, the correct answer is A.