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: Clinical evaluation included the use of the Unified Parkinson ' s Disease Rating Scale ( UPDRS ) , Hoehn _ Yahr score and Schwab England activities of daily living ( ADL ) score in ' on ' - and ' off ' - drug conditions before surgery and 6 months after surgery .
### Output Text:
Clinical evaluation included the use of the Unified Parkinson ' s Disease Rating Scale ( UPDRS ) , Hoehn _ Yahr score and Schwab England activities of daily living ( ADL ) score in ' on ' - and ' off ' - drug conditions before surgery and 6 months after surgery . 