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: Bolus MMC 10 mg / m ( 2 ) was added in 3 - weekly intervals .
### Output Text:
Bolus <span class="chemical">MMC</span> 10 mg / m ( 2 ) was added in 3 - weekly intervals . 