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: Clinical examinations and skin , oral and parenteral challenges with different corticosteroids and ELISA tests were performed .
### Output Text:
Clinical examinations and skin , oral and parenteral challenges with different <span class="chemical">corticosteroids</span> and ELISA tests were performed . 