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: The prevalences of adverse events were not significantly different between the 2 treatment groups ( T + A , 16 . 0 % [ 17 / 106 ] ; A , 15 . 4 % [ 16 / 104 ] ) .
### Output Text:
The prevalences of adverse events were not significantly different between the 2 treatment groups ( T + A , 16 . 0 % [ 17 / 106 ] ; A , 15 . 4 % [ 16 / 104 ] ) . 