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: In group 4 , a combination of cocaine and diazepam was administered simultaneously .
### Output Text:
In group 4 , a combination of <span class="chemical">cocaine</span> and <span class="chemical">diazepam</span> was administered simultaneously . 