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: The overall response rate ( World Health Organization [ WHO ] criteria ) was 15 % ( CR , 2 % ; PR 13 % ; 95 % CI , 6 % to 29 % ) .
### Output Text:
The overall response rate ( World Health Organization [ WHO ] criteria ) was 15 % ( CR , 2 % ; PR 13 % ; 95 % CI , 6 % to 29 % ) . 