$DNA$ is synthesized from viral $RNA$ using the enzyme:

If a hybrid $DNA$ $(^{14}N-^{15}N)$ is allowed to undergo replication twice in a medium containing nucleotides with $^{15}N$ base,then what proportion of light,heavy,and hybrid $DNA$ will be obtained respectively?

New $DNA$ synthesis occurs in the $P$ direction,and the $DNA$ polymerase enzyme reads the template in the $Q$ direction.
$\quad \quad \quad \quad P \quad \quad \quad \quad \quad Q$

$DNA$ repairing is primarily performed by which of the following enzymes?

Given below are two statements,one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A):$ $\text{DNA}$ replication occurs within a small opening of the $\text{DNA}$ helix,referred to as the replication fork.
Reason $(R):$ During transcription,the discontinuously synthesized fragments of $\text{DNA}$ are joined by the enzyme $\text{DNA}$ ligase.
In the light of the above statements,choose the most appropriate answer from the options given below:

The enzyme $DNA$ polymerase in $E. coli$ is a $DNA$-dependent polymerase and also has the ability to proof-read the $DNA$ strand being synthesized. Explain. Discuss the dual polymerase activity.