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: Male Sprague - Dawley rats were randomly assigned to a lead - treated group ( given lead acetate , 100 ppm , in drinking water and regular rat chow ) , a group given lead and vitamin E - fortified chow , or a normal control group given either regular food and water or vitamin E - fortified food for 12 weeks .
### Output Text:
Male Sprague - Dawley rats were randomly assigned to a <span class="chemical">lead</span> - treated group ( given <span class="chemical">lead acetate</span> , 100 ppm , in drinking water and regular rat chow ) , a group given <span class="chemical">lead</span> and <span class="chemical">vitamin E</span> - fortified chow , or a normal control group given either regular food and water or <span class="chemical">vitamin E</span> - fortified food for 12 weeks . 