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: BACKGROUND : Analysis of the literature for nonsteroidal anti - inflammatory drugs ( NSAIDs ) suggests that a low incidence of developmental anomalies occurs in rats given NSAIDs on specific days during organogenesis .
### Output Text:
BACKGROUND : Analysis of the literature for nonsteroidal anti - inflammatory drugs ( NSAIDs ) suggests that a low incidence of developmental anomalies occurs in rats given NSAIDs on specific days during organogenesis . 