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: These results indicate that delayed toxicity of CY in female DBA / 2 mice causes a bladder pathology that is not observed in C57BL / 6 mice .
### Output Text:
These results indicate that delayed toxicity of <span class="chemical">CY</span> in female DBA / 2 mice causes a bladder pathology that is not observed in C57BL / 6 mice . 