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: A randomized comparison of labetalol and nitroprusside for induced hypotension .
### Output Text:
A randomized comparison of <span class="chemical">labetalol</span> and <span class="chemical">nitroprusside</span> for induced hypotension . 