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: Additionally , WT mice were treated with a B2 receptor antagonist after cisplatin administration .
### Output Text:
Additionally , WT mice were treated with a B2 receptor antagonist after <span class="chemical">cisplatin</span> administration . 