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: RESULTS : Six of 30 patients ( 20 % ) without prior chemotherapy achieved a partial response ( PR ) ( 95 % confidence interval [ CI ] , 8 % to 39 % ) .
### Output Text:
RESULTS : Six of 30 patients ( 20 % ) without prior chemotherapy achieved a partial response ( PR ) ( 95 % confidence interval [ CI ] , 8 % to 39 % ) . 