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: Data on use of BZDs / RDs before admission , current medications and discharge diagnoses were collected from medical records .
### Output Text:
Data on use of <span class="chemical">BZDs</span> / RDs before admission , current medications and discharge diagnoses were collected from medical records . 