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: Mantle cell lymphoma ( MCL ) is a rare and aggressive type of B - cell non - Hodgkin ' s lymphoma .
### Output Text:
Mantle cell lymphoma ( MCL ) is a rare and aggressive type of B - cell non - Hodgkin ' s lymphoma . 