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: METHODS AND RESULTS : Adverse effects of Bpd requiring discontinuation of treatment were evaluated .
### Output Text:
METHODS AND RESULTS : Adverse effects of <span class="chemical">Bpd</span> requiring discontinuation of treatment were evaluated . 