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: METHODS : The objective of this study was to determine the feasibility , response rate , and toxicity of a paclitaxel , cisplatin , and gemcitabine combination to treat metastatic NSCLC .
### Output Text:
METHODS : The objective of this study was to determine the feasibility , response rate , and toxicity of a <span class="chemical">paclitaxel</span> , <span class="chemical">cisplatin</span> , and <span class="chemical">gemcitabine</span> combination to treat metastatic NSCLC . 