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: RESULTS : Sub - chronic GVG exposure inhibited the effect of cocaine for 3 days , which exceeded in magnitude and duration the identical acute dose .
### Output Text:
RESULTS : Sub - chronic <span class="chemical">GVG</span> exposure inhibited the effect of <span class="chemical">cocaine</span> for 3 days , which exceeded in magnitude and duration the identical acute dose . 