What is the mode of $DNA$ replication in $E. coli$?

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:

Experiments involving the use of radioactive thymidine to detect the distribution of newly synthesized $DNA$ in the chromosome were performed on which plant?

Which of the following serves a dual purpose in $DNA$ replication?

Give scientific reasons: $DNA$ replication is a semi-conservative process.

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