Which of the following bases is not present in $DNA$?

Select the correct sequence of True $(T)$ and False $(F)$ statements from the following:
$(i)$ $\text{Pentose sugar} + \text{base} \rightarrow \text{Nucleotide}$
$(ii)$ $\text{Nucleotide} + \text{phosphate} \rightarrow \text{Nucleoside}$
$(iii)$ $DNA$ contains four bases $A$,$G$,$C$ and $T$
$(iv)$ $RNA$ contains four bases $A$,$G$,$C$ and $U$.

In $DNA$,the base units are linked by which of the following?

The $AT/GC$ ratio in human beings is (where $A = \text{adenine}$,$T = \text{thymine}$,$G = \text{guanine}$,$C = \text{cytosine}$)

Assertion $(A)$: Adenine and guanine are present in $RNA$ as purine bases.
Reason $(R)$: The base uracil is present in $RNA$.
The correct option among the following is:

The double-helical structure of $DNA$ is due to the action of . . . . . . .