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: In TD group , three patients developed decreased auditory function , of which one presented with an auditory loss of - 30 dB , whereas in the OD group only one patient presented decreased auditory function .
### Output Text:
In TD group , three patients developed decreased auditory function , of which one presented with an auditory loss of - 30 dB , whereas in the OD group only one patient presented decreased auditory function . 