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: According to intention - to - treat , the overall response rate was 71 . 4 % ( 95 % CI , 53 . 7 - 85 . 4 % ) .
### Output Text:
According to intention - to - treat , the overall response rate was 71 . 4 % ( 95 % CI , 53 . 7 - 85 . 4 % ) . 