Anti-HIV drug combination that should not be used: (A) Zidovudine + Stavudine, (B) Atazanavir + Indinavir., (C) Didanosine/stavudine + Zalcitabine, (D) All of the above.
Answer is D. Anti-HIV drug combinations that should NOT be used are:

Zidovudine + Stavudine: Pharmacological antagonism (compete for intracellular phosphorylation)
Atazanavir + Indinavir: Additive unconjugated hyperbilirubinemia.
Didanosine/stavudine + Zalcitabine: Additive peripheral neuropathy.
Lamivudine + Zalcitabine: In vitro antagonism.