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: Carboplatin did not appear to add to the hematologic toxicities observed , and the paclitaxel / carboplatin combination could be dosed every 3 weeks .
### Output Text:
<span class="chemical">Carboplatin</span> did not appear to add to the hematologic toxicities observed , and the <span class="chemical">paclitaxel</span> / <span class="chemical">carboplatin</span> combination could be dosed every 3 weeks . 