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: Daucus carota extract ( 200 , 400 mg / kg , p . o . ) reduced significantly the brain acetylcholinesterase activity and cholesterol levels in young and aged mice .
### Output Text:
<span class="chemical">Daucus carota extract</span> ( 200 , 400 mg / kg , p . o . ) reduced significantly the brain acetylcholinesterase activity and <span class="chemical">cholesterol</span> levels in young and aged mice . 