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: However , when the patient was questioned about use of herbal products and supplements , the use of creatine monohydrate was revealed .
### Output Text:
However , when the patient was questioned about use of herbal products and supplements , the use of <span class="chemical">creatine</span> monohydrate was revealed . 