In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Pretreatment of animals with BNPP prior to APAP or PAP administration resulted in marked reduction of APAP ( 900 mg / kg ) nephrotoxicity but not PAP nephrotoxicity .
### Output Text:
Pretreatment of animals with <span class="chemical">BNPP</span> prior to <span class="chemical">APAP</span> or <span class="chemical">PAP</span> administration resulted in marked reduction of <span class="chemical">APAP</span> ( 900 mg / kg ) nephrotoxicity but not <span class="chemical">PAP</span> nephrotoxicity . 