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: On PND71 , a behavioral assay was performed using the elevated plus maze ( EPM ) and the light / dark test .
### Output Text:
On PND71 , a behavioral assay was performed using the elevated plus maze ( EPM ) and the light / dark test . 