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: We assessed the final efficacy and safety after reduction of ribavirin in groups A and B .
### Output Text:
We assessed the final efficacy and safety after reduction of <span class="chemical">ribavirin</span> in groups A and B . 