Q. Which of the following statements gives a correct explanation for the use of vectors containing drug resistance genes in the cloning of recombinant DNA (cDNA) molecules?

• (A) The products of the drug resistance genes protect the cDNA from destruction by the host cells
• (B) The drug resistance genes provide additional base sequences that enable the vector to accommodate larger inserts of cDNA
• (C) Entry of the vector containing the cDNA and the drug resistance genes into the host cell renders the latter identifiable as it is now resistant to antibiotic drugs
• (D) The cloned cDNA imparts drug resistance upon any cellular system with which it is used