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: At the same time , slightly increased creatine kinase ( CK ) levels were noted .
### Output Text:
At the same time , slightly increased <span class="chemical">creatine</span> kinase ( CK ) levels were noted . 