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: CONCLUSION : These results are consistent with a low level of activity of thalidomide in renal cell carcinoma .
### Output Text:
CONCLUSION : These results are consistent with a low level of activity of <span class="chemical">thalidomide</span> in renal cell carcinoma . 