The rapid appearance of HIV-1 strains that are resistant to AIDS drugs is due in part to which of the following property of its reverse transcriptase?

• A. AZT (zidovudine) is too expensive to be taken in effective doses
• B. The RNase H domain of p66 causes error prone synthesis
• C. It lacks a proofreading exonuclease
• D. It has low affinity for the correct dNTP's