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 examined whether female rats on various regimens of sugar access would show behavioral cross - sensitization to a low dose of amphetamine .
### Output Text:
The present study examined whether female rats on various regimens of sugar access would show behavioral cross - sensitization to a low dose of <span class="chemical">amphetamine</span> . 