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: Comparison of developmental toxicology of aspirin ( acetylsalicylic acid ) in rats using selected dosing paradigms .
### Output Text:
Comparison of developmental toxicology of <span class="chemical">aspirin</span> ( <span class="chemical">acetylsalicylic acid</span> ) in rats using selected dosing paradigms . 