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 : Two hundred sixty - five patients were included in this analysis ( n = 92 , 93 , and 80 for placebo , low dose , and high dose , respectively ) .
### Output Text:
RESULTS : Two hundred sixty - five patients were included in this analysis ( n = 92 , 93 , and 80 for placebo , low dose , and high dose , respectively ) . 