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: Half - relaxation time was prolonged in both steroid groups , and time to peak tension was longer with M , whereas tetanic tensions were similar .
### Output Text:
Half - relaxation time was prolonged in both <span class="chemical">steroid</span> groups , and time to peak tension was longer with <span class="chemical">M</span> , whereas tetanic tensions were similar . 