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: It appears from these data that hematologic work - ups may be useful in women who are about to start long - term oral contraceptive therapy .
### Output Text:
It appears from these data that hematologic work - ups may be useful in women who are about to start long - term <span class="chemical">oral contraceptive</span> therapy . 