The correct option is A Uracil
Ribonucleotides are components of RNA while deoxyribonucleotides are components of DNA. Ribonucleotides are made up of ribose sugar, nitrogenous base and phosphate.The nitrogenous bases in ribonucleotides are adenine, guanine, cytosine and uracil (instead of thymine base which is found in DNA, rest of the bases are same).