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: To assess the safety of the ACE inhibitor enalapril a multicenter , randomized , prazosin - controlled trial was designed that compared the incidence and severity of symptomatic hypotension on the first day of treatment .
### Output Text:
To assess the safety of the <span class="chemical">ACE inhibitor</span> <span class="chemical">enalapril</span> a multicenter , randomized , <span class="chemical">prazosin</span> - controlled trial was designed that compared the incidence and severity of symptomatic hypotension on the first day of treatment . 