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Here , we investigated pathway regulation upon in vivo B [ a ] P exposure of wild - type and Xpa ( - / - ) p53 ( + / - ) mice .
 Chemical: B [ a ] P
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: B [ a ] P