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

Read the following statements and choose the set of correct statements:

$(a)$ Euchromatin is loosely packed chromatin

$(b)$ Heterochromatin is transcriptionally active

$(c)$ Histone octomer is wrapped by negatively charged DNA in nucleosome

$(d)$ Histones are rich in lysine and arginine

$(e)$ A typical nucleosome contains $400\,bp$ of DNA helix

Choose the correct answer from the options given below:

Uridine monophosphate is found in

The successive nucleotides of $RNA$ are covalently linked through or antiparallal

Give the historical background of $DNA.$