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: A case is reported of the hemolytic uremic syndrome ( HUS ) in a woman taking oral contraceptives .
### Output Text:
A case is reported of the hemolytic uremic syndrome ( HUS ) in a woman taking <span class="chemical">oral contraceptives</span> . 