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: There was no significant difference in the proportion of subjects in the DFMO plus sulindac group who experienced clinically significant hearing loss compared with the placebo group .
### Output Text:
There was no significant difference in the proportion of subjects in the <span class="chemical">DFMO</span> plus <span class="chemical">sulindac</span> group who experienced clinically significant hearing loss compared with the placebo group . 