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: Both patients were also hypothyroid , but it is not clear whether this was a predisposing factor to the development of these adverse reactions .
### Output Text:
Both patients were also hypothyroid , but it is not clear whether this was a predisposing factor to the development of these adverse reactions . 