This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'MDR gene acts by: \nSelect and explain. \nA. Block drug activation, B. Block intracellular DNA synthesis, C. Cause efflux of drug, D. DNA repair inhibition', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Cause efflux of drug', 'role': 'assistant'}]