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 three significant predictors of dyskinesia were duration of levodopa therapy , onset age , and total daily levodopa dose .
### Output Text:
The three significant predictors of dyskinesia were duration of <span class="chemical">levodopa</span> therapy , onset age , and total daily <span class="chemical">levodopa</span> dose . 