Who used heavy nitrogen $N^{15}$ for proving the semiconservative way of $DNA$ replication?

Bacteria were grown in a medium containing a heavy isotope of nitrogen $(^{15}N)$ for many generations,and all their $DNA$ contained only heavy nitrogen. $A$ bacterium of this type was transferred to a normal medium and allowed to duplicate. After two divisions,the distribution of heavy $DNA$ is likely to be:

How many types of $DNA$ polymerases are present in bacteria?

Which of the following processes is related to reverse transcription?

In the process of $DNA$ replication,deoxyribonucleoside triphosphates act as:

Given below are two statements:
Statement $I:$
$DNA$ polymerases catalyse polymerisation only in one direction,that is $5^{\prime} \rightarrow 3^{\prime}$.
Statement $II:$
During replication of $DNA$,on one strand the replication is continuous while on the other strand it is discontinuous.
In the light of the above statements,choose the correct answer from the options given below: