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: OBJECTIVE : The objective was to examine the relation between vitamin C intake and mortality from cardiovascular disease .
### Output Text:
OBJECTIVE : The objective was to examine the relation between <span class="chemical">vitamin C</span> intake and mortality from cardiovascular disease . 