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: An objective response was observed in 73 . 5 % of the patients ( 95 % confidence interval [ CI ] , 55 . 6 - 87 . 1 % ) , including 4 complete responses ( 11 . 7 % ) .
### Output Text:
An objective response was observed in 73 . 5 % of the patients ( 95 % confidence interval [ CI ] , 55 . 6 - 87 . 1 % ) , including 4 complete responses ( 11 . 7 % ) . 