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: In Parkinson ' s disease + LID , the force involved in pressing down the object before lifting was significantly increased by levodopa ( by 61 % , P < 0 . 05 ) .
### Output Text:
In Parkinson ' s disease + LID , the force involved in pressing down the object before lifting was significantly increased by <span class="chemical">levodopa</span> ( by 61 % , P < 0 . 05 ) . 