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: The MFL regimen achieves little palliative benefit and induces severe toxicity at a fairly high rate .
### Output Text:
The <span class="chemical">MFL regimen</span> achieves little palliative benefit and induces severe toxicity at a fairly high rate . 