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: Rather , BNPP pretreatment reduced the fraction of APAP excreted as PAP by 64 and 75 % after APAP doses of 750 and 900 mg / kg .
### Output Text:
Rather , <span class="chemical">BNPP</span> pretreatment reduced the fraction of <span class="chemical">APAP</span> excreted as <span class="chemical">PAP</span> by 64 and 75 % after <span class="chemical">APAP</span> doses of 750 and 900 mg / kg . 