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: Hepatic adenomas and focal nodular hyperplasia of the liver in young women on oral contraceptives : case reports .
### Output Text:
Hepatic adenomas and focal nodular hyperplasia of the liver in young women on <span class="chemical">oral contraceptives</span> : case reports . 