The mode of $DNA$ replication in $E. coli$ is:

Primase is a type of ...........

Given below are the two statements.
Statement $I$: In prokaryotes,there is only one replicon,however,in eukaryotes,there are several replicons in tandem.
Statement $II$: The two separated strands in a replicon of $DNA$ are prevented from rejoining by helicase enzyme.
In the light of the above statements,choose the correct answer from the options given below.

The semi-conservative replication of $DNA$ was proven in:

$E. coli$ bacteria grown in ${}^{15}NH_4Cl$ medium for several generations are allowed to grow in ${}^{14}NH_4Cl$ medium. After $2$ generations,the density gradient of the isolated $DNA$ is:

Complementary $DNA$ $(cDNA)$ is complementary to