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: However , 10 of 37 patients with reduction of ribavirin could not continue combination therapy because their < 8 . 5 g / dl hemoglobin values decreased to or anemia - related severe side effects occurred ( group B ) .
### Output Text:
However , 10 of 37 patients with reduction of <span class="chemical">ribavirin</span> could not continue combination therapy because their < 8 . 5 g / dl hemoglobin values decreased to or anemia - related severe side effects occurred ( group B ) . 