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: Within the last several years , previously rare liver tumors have been seen in young women using oral contraceptive steroids .
### Output Text:
Within the last several years , previously rare liver tumors have been seen in young women using <span class="chemical">oral contraceptive</span> <span class="chemical">steroids</span> . 