Answer:
The correct answer is D. A replication bubble is the site of DNA replication.
Step-by-step explanation:
For DNA replication to occur, the two strands of the DNA must unwind at the site of replication. This site of replication where the DNA strands unwinds for replication is termed as replication bubble. Hence, D is the correct option.
Other options like C is incorrect because DNA polymerase is the enzyme that is involved in DNA replication, as it is not the site for DNA replication. Option B is incorrect because double helix is referred as the two strands of DNA coiled up as a double helix. Option A is incorrect because a replicon is the DNA that has been produced by replication of a single strand of DNA.