3tc is an antiretroviral treatment used to prevent hiv infection from becoming aids. after treatment with 3tc, the hiv population in a patient consists entirely of 3tc-resistant virus particles. what best explain this phenomenon? a) hiv can change its surface proteins through mutations and resist vaccines. b) the patient became re-infected with 3tc-resistant viruses after the initial exposure. c) the drug caused rna changes to occur, creating a resistance to the once-applicable drug. d) a few drug-resistant viruses were present at the start of treatment and selective pressures increased their frequency.