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: Cortical maps revealed severe gray - matter deficits in the cingulate , limbic , and paralimbic cortices of MA abusers ( averaging 11 . 3 % below control ; p < 0 . 05 ) .
### Output Text:
Cortical maps revealed severe gray - matter deficits in the cingulate , limbic , and paralimbic cortices of <span class="chemical">MA</span> abusers ( averaging 11 . 3 % below control ; p < 0 . 05 ) . 