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: Flumazenil was found to promptly reverse sedation induced by diazepam in the presence of opioids .
### Output Text:
<span class="chemical">Flumazenil</span> was found to promptly reverse sedation induced by <span class="chemical">diazepam</span> in the presence of opioids . 