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: The present study aimed to explore the effect of MT induction on carmustine ( BCNU ) - induced hippocampal cognitive dysfunction in rats .
### Output Text:
The present study aimed to explore the effect of <span class="chemical">MT</span> induction on <span class="chemical">carmustine</span> ( <span class="chemical">BCNU</span> ) - induced hippocampal cognitive dysfunction in rats . 