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: This study investigates the role of ILK in liver enlargement induced by phenobarbital ( PB ) .
### Output Text:
This study investigates the role of ILK in liver enlargement induced by <span class="chemical">phenobarbital</span> ( <span class="chemical">PB</span> ) . 