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: CaCO3 dosage , calculated dietary calcium intake , and circulating levels of vitamin D metabolites were similar in both groups .
### Output Text:
<span class="chemical">CaCO3</span> dosage , calculated dietary <span class="chemical">calcium</span> intake , and circulating levels of <span class="chemical">vitamin D</span> metabolites were similar in both groups . 