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: The present studies demonstrate that growth and vitamin D treatment enhance the extent of artery calcification in rats given sufficient doses of Warfarin to inhibit gamma - carboxylation of matrix Gla protein , a calcification inhibitor known to be expressed by smooth muscle cells and macrophages in the artery wall .
### Output Text:
The present studies demonstrate that growth and <span class="chemical">vitamin D</span> treatment enhance the extent of artery calcification in rats given sufficient doses of <span class="chemical">Warfarin</span> to inhibit gamma - carboxylation of matrix Gla protein , a calcification inhibitor known to be expressed by smooth muscle cells and macrophages in the artery wall . 