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: RESULTS : ROSC was achieved in only one of the control piglets compared with most of the treated piglets .
### Output Text:
RESULTS : ROSC was achieved in only one of the control piglets compared with most of the treated piglets . 