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: Nimodipine prevents memory impairment caused by nitroglycerin - induced hypotension in adult mice .
### Output Text:
<span class="chemical">Nimodipine</span> prevents memory impairment caused by <span class="chemical">nitroglycerin</span> - induced hypotension in adult mice . 