Which of the following is a nucleoside?

The figure gives an important concept in the genetic implication of $DNA$. Fill the blanks $A, B$ and $C$.

In his experiments on the chemistry of $DNA$, Chargaff estimated the base composition of human sperms and found that Adenine constituted $31\%$ and Guanine $19\%$. The quantity of Cytosine in the $DNA$ of human somatic cell is likely to be

In the $DNA$ molecule,

The association of histone $H_1$ with a nucleosome indicates that