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: Wild - type ( WT ) and ILK : liver - / - mice were given PB ( 0 . 1 % in drinking water ) for 10 days .
### Output Text:
Wild - type ( WT ) and ILK : liver - / - mice were given <span class="chemical">PB</span> ( 0 . 1 % in drinking water ) for 10 days . 