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 potential modifying effect of retinyl acetate ( RA ) on butylated hydroxyanisole ( BHA ) - induced rat forestomach tumorigenesis was examined .
### Output Text:
The potential modifying effect of <span class="chemical">retinyl acetate</span> ( <span class="chemical">RA</span> ) on <span class="chemical">butylated hydroxyanisole</span> ( <span class="chemical">BHA</span> ) - induced rat forestomach tumorigenesis was examined . 