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: BACKGROUND : Bepridil hydrochloride ( Bpd ) has attracted attention as an effective drug for atrial fibrillation ( AF ) and atrial flutter ( AFL ) .
### Output Text:
BACKGROUND : <span class="chemical">Bepridil hydrochloride</span> ( <span class="chemical">Bpd</span> ) has attracted attention as an effective drug for atrial fibrillation ( AF ) and atrial flutter ( AFL ) . 