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: AChE activity was significantly decreased in the hippocampus of mice with BPA compared to control mice , whereas no difference was found in the prefrontal cortex , hypothalamus and cerebellum .
### Output Text:
AChE activity was significantly decreased in the hippocampus of mice with <span class="chemical">BPA</span> compared to control mice , whereas no difference was found in the prefrontal cortex , hypothalamus and cerebellum . 