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: Two cases of hepatic adenoma and one of focal nodular hyperplasia presumably associated with the use of oral contraceptives , are reported .
### Output Text:
Two cases of hepatic adenoma and one of focal nodular hyperplasia presumably associated with the use of <span class="chemical">oral contraceptives</span> , are reported . 