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: Health , physical abilities and cognitive function were compared between BZD / RD users and non - users , and adjustments were made for confounding variables .
### Output Text:
Health , physical abilities and cognitive function were compared between BZD / RD users and non - users , and adjustments were made for confounding variables . 