Given below is the diagrammatic representation of one of the categories of small molecular weight organic compounds in the living tissues. Identify the category shown and the one blank component 'X' in it <br>

Question

https://clay6.com/mpaimg/n54.jpg

( A ) Nucleotide - Adenine
( B ) Amino acid - $NH_2$
( C ) Nucleoside - Uracil
( D ) Cholesterol -Guanin