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: Carotid arteries , vena cava , and sympathetic ganglia from LNNA rats had higher basal levels of superoxide compared with those from control rats .
### Output Text:
Carotid arteries , vena cava , and sympathetic ganglia from <span class="chemical">LNNA</span> rats had higher basal levels of <span class="chemical">superoxide</span> compared with those from control rats . 