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: Third group received BCNU ( 20 mg / kg , i . v , once ) 24 h after injection with normal saline ( i . c . v ) .
### Output Text:
Third group received <span class="chemical">BCNU</span> ( 20 mg / kg , i . v , once ) 24 h after injection with normal saline ( i . c . v ) . 