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: CONCLUSION : In utero , exposure to tobacco smoking seems to have a small impact on outer hair cells .
### Output Text:
CONCLUSION : In utero , exposure to tobacco <span class="chemical">smoking</span> seems to have a small impact on outer hair cells . 