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: Rats were treated with the NO synthase inhibitor LNNA ( 0 . 5 g / L in drinking water ) for 2 weeks .
### Output Text:
Rats were treated with the <span class="chemical">NO</span> synthase inhibitor <span class="chemical">LNNA</span> ( 0 . 5 g / L in drinking water ) for 2 weeks . 