Answer:
reverse transcriptases.
Explanation:
Reverse transcriptase is an enzyme that makes DNA copies of the RNA template. To make the libraries of the genes that are expressed, the enzyme reverse transcriptase is used. The researcher first extracts mRNA from the cells of target organisms and then uses the enzyme reverse transcriptase to prepare complementary DNAs which are also called cDNAs. The enzyme reverse transcriptase add dNTPs to make a complementary DNA strands.