Answer:
(B) mRNA → cDNA.
Step-by-step explanation:
Reverse transcriptase can be defined as an enzyme, which makes cDNA (complementary DNA) by using mRNA as a template. These enzymes are also known as RNA dependent DNA synthase as they make DNA by using information present in RNA.
These enzymes are used by eukaryotes (as telomerase) to replicate chromosome ends or telomeres, by retrotransposon, and by some viruses, such as retroviruses to replicate their genetic material.
Thus, the correct answer is option (B).