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: Rate of body weight gain was depressed in the P100 , FR , and P10 groups compared with the S group .
### Output Text:
Rate of body weight gain was depressed in the P100 , FR , and P10 groups compared with the S group . 