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: Further , we show that mice genetically engineered to be deficient in brain DA develop METH neurotoxicity , as long as the thermic effects of METH are preserved .
### Output Text:
Further , we show that mice genetically engineered to be deficient in brain <span class="chemical">DA</span> develop <span class="chemical">METH</span> neurotoxicity , as long as the thermic effects of <span class="chemical">METH</span> are preserved . 