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: Animals became somnolent after diazepam and then active after flumazenil administration .
### Output Text:
Animals became somnolent after <span class="chemical">diazepam</span> and then active after <span class="chemical">flumazenil</span> administration . 