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: Paclitaxel combined with carboplatin in the first - line treatment of advanced ovarian cancer .
### Output Text:
<span class="chemical">Paclitaxel</span> combined with <span class="chemical">carboplatin</span> in the first - line treatment of advanced ovarian cancer . 