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: There was no correlation between vitamin B12 or folate levels and development of myelosuppression .
### Output Text:
There was no correlation between <span class="chemical">vitamin B12</span> or <span class="chemical">folate</span> levels and development of myelosuppression . 