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: Preliminary studies suggest that statins could interfere with the risk of recurrence after electrical cardioversion .
### Output Text:
Preliminary studies suggest that <span class="chemical">statins</span> could interfere with the risk of recurrence after electrical cardioversion . 