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: The motor score of the Unified Parkinson ' s Disease Rating Scale , a dyskinesia score and force in a grip - lift paradigm were assessed ON and OFF levodopa .
### Output Text:
The motor score of the Unified Parkinson ' s Disease Rating Scale , a dyskinesia score and force in a grip - lift paradigm were assessed ON and OFF <span class="chemical">levodopa</span> . 