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 corresponding absolute risk of VTE was 3 . 4 ( range , 3 . 1 - 3 . 8 ) per 10 000 women years among the women on COCs , 4 . 2 ( range , 3 . 2 - 5 . 2 ) per 10 000 women years among women on levonorgestrel - containing COCs , and 3 . 1 ( range , 1 . 3 - 4 . 9 ) per 10 000 women years among the women on CPA / EE .
### Output Text:
The corresponding absolute risk of VTE was 3 . 4 ( range , 3 . 1 - 3 . 8 ) per 10 000 women years among the women on <span class="chemical">COCs</span> , 4 . 2 ( range , 3 . 2 - 5 . 2 ) per 10 000 women years among women on <span class="chemical">levonorgestrel</span> - containing <span class="chemical">COCs</span> , and 3 . 1 ( range , 1 . 3 - 4 . 9 ) per 10 000 women years among the women on <span class="chemical">CPA</span> / <span class="chemical">EE</span> . 