Answer:
B-cytosine
Explanation:
DNA methylation is the addition of methyl group to the DNA which further modifying function of genes and the affecting gene expression.
Out of the two of the DNA's four bases, the bases that can be methylated are cytosine and adenine.
In humans, the most widely DNA methylation is covalent addition of methyl group at 5-carbon of cytosine ring which results in 5-methylcytosine.
