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: After adjustment for these variables as confounders , use of BZDs / RDs was not associated with cognitive function as measured by the MMSE .
### Output Text:
After adjustment for these variables as confounders , use of <span class="chemical">BZDs</span> / RDs was not associated with cognitive function as measured by the MMSE . 