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 choline acetyltransferase ( ChAT ) activator , which enhances cholinergic transmission via an augmentation of the enzymatic production of acetylcholine ( ACh ) , is an important factor in the treatment of Alzheimer ' s disease ( AD ) .
### Output Text:
The <span class="chemical">choline</span> acetyltransferase ( ChAT ) activator , which enhances cholinergic transmission via an augmentation of the enzymatic production of <span class="chemical">acetylcholine</span> ( <span class="chemical">ACh</span> ) , is an important factor in the treatment of Alzheimer ' s disease ( AD ) . 