The best answer is C - nucleotides.
A nucleotide is a small unit (subunit) of DNA or RNA. It is made up of a nitrogenous base, a phosphate molecule and a sugar molecule .
There four kinds of nitrogenous bases called adenine, cytosine, guanine and thymine. They are similar in both DNA and RNA with one exception. In RNA, thymine is not there, instead it is replaced with another type of nitrogenous base called uracil.
Thousands of nucleotides are linked to form a DNA or RNA molecule.