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: A search of the literature on the thromboembolic complications of CC does not include this severe ophthalmic complication , although mild visual disturbance after CC intake is not uncommon .
### Output Text:
A search of the literature on the thromboembolic complications of <span class="chemical">CC</span> does not include this severe ophthalmic complication , although mild visual disturbance after <span class="chemical">CC</span> intake is not uncommon . 