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: METHODS : This comparative , Phase III , 12 - week , multicenter , prospective , randomized , double - blind study was conducted in Indian patients aged 18 to 65 years with established stage II hypertension .
### Output Text:
METHODS : This comparative , Phase III , 12 - week , multicenter , prospective , randomized , double - blind study was conducted in Indian patients aged 18 to 65 years with established stage II hypertension . 