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: Vitamin E supplementation had no effect on either blood pressure , plasma MDA , or NOS expression in the control group .
### Output Text:
<span class="chemical">Vitamin E</span> supplementation had no effect on either blood pressure , plasma <span class="chemical">MDA</span> , or NOS expression in the control group . 