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: Mechanisms of hypertension induced by nitric oxide ( NO ) deficiency : focus on venous function .
### Output Text:
Mechanisms of hypertension induced by <span class="chemical">nitric oxide</span> ( <span class="chemical">NO</span> ) deficiency : focus on venous function . 