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: The adjusted odds ratio was 2 . 5 ( 95 percent confidence interval , 1 . 5 to 4 . 1 ) among women who used second - generation oral contraceptives and 1 . 3 ( 95 percent confidence interval , 0 . 7 to 2 . 5 ) among those who used third - generation oral contraceptives .
### Output Text:
The adjusted odds ratio was 2 . 5 ( 95 percent confidence interval , 1 . 5 to 4 . 1 ) among women who used second - generation <span class="chemical">oral contraceptives</span> and 1 . 3 ( 95 percent confidence interval , 0 . 7 to 2 . 5 ) among those who used third - generation <span class="chemical">oral contraceptives</span> . 