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
All are chemical carcinogens except 
Select and explain. 
A. Beta carotene, B. Benzene, C. Thorostat, D. Nitrates
A: Beta carotene
Answer: A: Beta carotene 
Explanation: 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