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: This model can be used alone or in combination with other drugs to explore the effect of CBDCA on the peripheral nervous system .
### Output Text:
This model can be used alone or in combination with other drugs to explore the effect of <span class="chemical">CBDCA</span> on the peripheral nervous system . 