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 [ complete response ( CR ) plus partial response ( PR ) ] across all dose levels was 77 % , with a 10 % CR rate .
### Output Text:
The overall response rate [ complete response ( CR ) plus partial response ( PR ) ] across all dose levels was 77 % , with a 10 % CR rate . 