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 an attempt to overcome this problem , a clinical trial of CB 3717 administered with alkaline diuresis is under way .
### Output Text:
In an attempt to overcome this problem , a clinical trial of <span class="chemical">CB 3717</span> administered with alkaline diuresis is under way . 