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: Rates of response and BP control were significantly higher in the groups that received combination treatment compared with those that received monotherapy .
### Output Text:
Rates of response and BP control were significantly higher in the groups that received combination treatment compared with those that received monotherapy . 