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: The subject , a 31 - year - old female smoker , was participating in a clinical trial evaluating an investigational medication for smoking cessation that used sustained - release bupropion as an active control .
### Output Text:
The subject , a 31 - year - old female smoker , was participating in a clinical trial evaluating an investigational medication for smoking cessation that used sustained - release <span class="chemical">bupropion</span> as an active control . 