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: CONCLUSIONS : These results suggest that differences in cholinergic activity and postsynaptic sensitivity to cholinergic convulsants may be associated with ethanol withdrawal severity and implicate cholinergic mechanisms in alcohol withdrawal .
### Output Text:
CONCLUSIONS : These results suggest that differences in cholinergic activity and postsynaptic sensitivity to cholinergic convulsants may be associated with <span class="chemical">ethanol</span> withdrawal severity and implicate cholinergic mechanisms in <span class="chemical">alcohol</span> withdrawal . 