This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neoplasia, Subject name: Pathology
[{'content': 'All are chemical carcinogens except \nSelect and explain. \nA. Beta carotene, B. Benzene, C. Thorostat, D. Nitrates', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a (Betacarotene). (Ref. Robbin Pathology, 6th ed., 307)CHEMICAL CARCINOGENSDirect actingProcarcinogensOthersa-propiolactoneBenzopyreneThorostatDimethyl sulfateDibenzanthraceneNitrosamineDiepoxybutane3-methyl cholanthrineVinyl chlorideAnticancerous drugsAromatic aminesNickel1-acetyl imidazoleAmidesChromiumDimethyl carbamyl chlorideAzo dyesInsecticides BenzidineFungicides a-naphthlaminePolychlorinated biphenyls Aflatoxin B1 Griseofulvin Betel nuts Safrole Cycasin', 'role': 'assistant'}]