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 : Forty - two patients completed the study , 22 in Group A and 20 in Group B .
### Output Text:
RESULTS : Forty - two patients completed the study , 22 in Group A and 20 in Group B . 