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: Of these , nearly half ( n = 78 ) had used BZDs / RDs before admission , and the remainder ( n = 86 ) were non - users .
### Output Text:
Of these , nearly half ( n = 78 ) had used <span class="chemical">BZDs</span> / RDs before admission , and the remainder ( n = 86 ) were non - users . 