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: When participants were stratified by antiretroviral therapy ( ART ) use , the association between alcohol and CD4 + T - cell did not reach statistical significance .
### Output Text:
When participants were stratified by antiretroviral therapy ( ART ) use , the association between <span class="chemical">alcohol</span> and CD4 + T - cell did not reach statistical significance . 