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: One of 16 patients ( 6 % ) with prior chemotherapy had a complete response ( CR ) of 31 weeks ' duration ( 95 % CI , 0 % to 30 % ) .
### Output Text:
One of 16 patients ( 6 % ) with prior chemotherapy had a complete response ( CR ) of 31 weeks ' duration ( 95 % CI , 0 % to 30 % ) . 