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: A 65 - year - old woman was treated with extended - release verapamil 240 mg / d .
### Output Text:
A 65 - year - old woman was treated with extended - release <span class="chemical">verapamil</span> 240 mg / d . 