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: RESULTS : There were no group differences in psychopathology or " eyes task " performance , but the RC group , who otherwise had similar illicit substance use histories to the OC group , exhibited impaired fear recognition accuracy compared to the OC and CN groups .
### Output Text:
RESULTS : There were no group differences in psychopathology or " eyes task " performance , but the RC group , who otherwise had similar illicit substance use histories to the OC group , exhibited impaired fear recognition accuracy compared to the OC and CN groups . 