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: Thus , two control groups were generated : group C1 , which included age - and sex - comparable lithium - treated bipolar normocalcemic patients , and group C2 , which included bipolar normocalcemic patients treated with anticonvulsant mood stabilizers .
### Output Text:
Thus , two control groups were generated : group C1 , which included age - and sex - comparable <span class="chemical">lithium</span> - treated bipolar normocalcemic patients , and group C2 , which included bipolar normocalcemic patients treated with anticonvulsant mood stabilizers . 