This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Which vitamin is synthesized by intestinal sites? 
Select and explain. 
A. Vit B, B. Vit A, C. Vit D, D. Vit K
D: Vit K
Answer: D: Vit K 
Explanation: Three compounds have the biological activity of vitamin K phylloquinone, the normal dietary source, found in green vegetables; menaquinones, synthesized by intestinal bacteria, menadione and menadiol diacetate, synthetic compounds that can be metabolized to phylloquinone menaquinone is synthesized in the intestinal site by the intestinal bacteria Ref: Harper 30e, page: 554