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 control rats received atropine sulfate , but also saline and olive oil instead of other antidotes and DFP , respectively .
### Output Text:
The control rats received <span class="chemical">atropine sulfate</span> , but also saline and olive oil instead of other antidotes and <span class="chemical">DFP</span> , respectively . 