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: Among the 34 patients evaluable for response , there were three complete responses ( 9 % ) and 18 partial responses ( 53 % ) for an overall response rate of 62 % .
### Output Text:
Among the 34 patients evaluable for response , there were three complete responses ( 9 % ) and 18 partial responses ( 53 % ) for an overall response rate of 62 % . 