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: Newborns whose mothers reported smoking during pregnancy ( n = 200 ears ) were compared to a control group of newborns ( n = 200 ears ) , whose mothers were non - smokers .
### Output Text:
Newborns whose mothers reported <span class="chemical">smoking</span> during pregnancy ( n = 200 ears ) were compared to a control group of newborns ( n = 200 ears ) , whose mothers were non - smokers . 