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: Neither dosage nor serum levels of CBZ were in a higher range .
### Output Text:
Neither dosage nor serum levels of <span class="chemical">CBZ</span> were in a higher range . 