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: Pregnant rats were given either vehicle or 2 daily intraperitoneal injections of dexamethasone ( 0 . 2 mg / kg body weight ) on gestational days 11 and 12 , 13 and 14 , 15 and 16 , 17 and 18 , or 19 and 20 .
### Output Text:
Pregnant rats were given either vehicle or 2 daily intraperitoneal injections of <span class="chemical">dexamethasone</span> ( 0 . 2 mg / kg body weight ) on gestational days 11 and 12 , 13 and 14 , 15 and 16 , 17 and 18 , or 19 and 20 . 