2347
The relative toxicity of nickel oxide ( NiO ) , nickel sulfate hexahydrate ( NiSO4 . 6H2O ) , and nickel subsulfide ( Ni3S2 ) was studied in F344 / N rats and B6C3F1 mice after inhalation exposure for 6 hr / day , 5 days / week , for 13 weeks .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
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