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: Extra caution is warranted in treating infertility patients with CC , and patients should be well informed of this side effect before commencement of therapy .
### Output Text:
Extra caution is warranted in treating infertility patients with <span class="chemical">CC</span> , and patients should be well informed of this side effect before commencement of therapy . 