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 of nontraumatic dissecting aneurysm of the basilar artery in association with hypertension , smoke , and oral contraceptives is reported in a young female patient with a locked - in syndrome .
### Output Text:
A case of nontraumatic dissecting aneurysm of the basilar artery in association with hypertension , smoke , and <span class="chemical">oral contraceptives</span> is reported in a young female patient with a locked - in syndrome . 