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: DESIGN : Male Sprague - Dawley rats received 100 mg / kg cocaine IP alone , 5 mg / kg diazepam alone , or a combination of diazepam and cocaine .
### Output Text:
DESIGN : Male Sprague - Dawley rats received 100 mg / kg <span class="chemical">cocaine</span> IP alone , 5 mg / kg <span class="chemical">diazepam</span> alone , or a combination of <span class="chemical">diazepam</span> and <span class="chemical">cocaine</span> . 