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: OBJECTIVE : To achieve absolute risk estimates of venous thromboembolism ( VTE ) among women on cyproterone acetate plus ethinylestradiol ( CPA / EE ) , and among women on combined oral contraceptives ( COCs ) .
### Output Text:
OBJECTIVE : To achieve absolute risk estimates of venous thromboembolism ( VTE ) among women on <span class="chemical">cyproterone acetate</span> plus <span class="chemical">ethinylestradiol</span> ( <span class="chemical">CPA</span> / <span class="chemical">EE</span> ) , and among women on <span class="chemical">combined oral contraceptives</span> ( <span class="chemical">COCs</span> ) . 