Concept:The word “resistant” describes the ability to withstand the effect of a drug or substance.
Explanation:Quinine is a drug used against malaria parasites.
The sentence shows that the parasites are no longer affected by it.
“Resistant” is the natural word used when parasites or organisms survive despite a drug's action.
“Immune” refers to a living body being protected from a disease, not to parasites resisting a drug.
“Opposed” and “defiant” do not correctly describe the effect of quinine on parasites.
Therefore, the best word to complete the sentence is “resistant”.
Answer:A. resistant