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: Objective response ( > PR ( partial response ) ) rate was 77 . 4 % ( complete response ( CR ) , 20 . 2 % ) .
### Output Text:
Objective response ( > PR ( partial response ) ) rate was 77 . 4 % ( complete response ( CR ) , 20 . 2 % ) . 