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: Levodopa ( 15 mg / kg and benserazide , 3 . 75 mg / kg ) p . o .
### Output Text:
<span class="chemical">Levodopa</span> ( 15 mg / kg and <span class="chemical">benserazide</span> , 3 . 75 mg / kg ) p . o . 