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 purpose of this study was to delineate the role of CE in the combined cardiotoxicity of cocaine and ethanol in a model simulating their abuse .
### Output Text:
The purpose of this study was to delineate the role of <span class="chemical">CE</span> in the combined cardiotoxicity of <span class="chemical">cocaine</span> and <span class="chemical">ethanol</span> in a model simulating their abuse . 