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: Rats were stratified into control groups and ADR - induced nephropathy groups .
### Output Text:
Rats were stratified into control groups and <span class="chemical">ADR</span> - induced nephropathy groups . 