cytosine (C); a nitrogenous base that pairs with [[鸟嘌呤|鳥嘌呤|niao3 piao4 ling4]] in DNA and RNA (sometimes also used to refer to the nucleoside or nucleotide)

uracil; a chemical base that pairs with [[腺嘌呤|腺嘌呤|xian4 piao4 ling4]] in RNA

a pyrimidine nucleobase (T) that pairs with [[腺嘌呤|腺嘌呤|xian4 piao4 ling4]] in DNA