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: Mean serum potassium level fell , and urea and uric acid levels rose , in men and women taking bendrofluazide .
### Output Text:
Mean serum <span class="chemical">potassium</span> level fell , and <span class="chemical">urea</span> and <span class="chemical">uric acid</span> levels rose , in men and women taking <span class="chemical">bendrofluazide</span> . 