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 is a benzodiazepine receptor antagonist used to reverse sedation and respiratory depression induced by benzodiazepines .
### Output Text:
<span class="chemical">Flumazenil</span> is a <span class="chemical">benzodiazepine</span> receptor antagonist used to reverse sedation and respiratory depression induced by <span class="chemical">benzodiazepines</span> . 