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: Early identification of fetal alcohol exposure and maternal abstinence led to better infant outcomes .
### Output Text:
Early identification of fetal <span class="chemical">alcohol</span> exposure and maternal abstinence led to better infant outcomes . 