Which one of the following correctly represents the manner of replication of $DNA$?

$^{15}N$ labeled $E. coli$ is allowed to grow in a $^{14}N$ medium. The two strands of the $DNA$ molecule of the first generation bacteria have:

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

Replication was allowed to take place in the presence of radioactive deoxynucleotide precursors in $E. coli$ that was a mutant for $DNA$ ligase. Newly synthesised radioactive $DNA$ was purified and strands were separated by denaturation. These were centrifuged using density gradient centrifugation. Which of the following would be a correct result?

Identify the enzymes that synthesize $DNA$ from $RNA$.

During $DNA$ replication,why is it that the entire molecule does not open in one go? Explain the replication fork. What are the two functions that the monomers $(dNTPs)$ play?