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: The association between alcohol consumption and depression was significant ( p < 0 . 001 ) .
### Output Text:
The association between <span class="chemical">alcohol</span> consumption and depression was significant ( p < 0 . 001 ) . 