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: Behavioral effects of diazepam and propranolol in patients with panic disorder and agoraphobia .
### Output Text:
Behavioral effects of <span class="chemical">diazepam</span> and <span class="chemical">propranolol</span> in patients with panic disorder and agoraphobia . 