This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Malnutrition, Subject name: Pediatrics
A three day-old term infant borne at home, breast-fed exclusively, presented with lethargy, bulging fontanel, and bright red blood from rectum. What is the most likely etiology of his disease? 
Select and explain. 
A. Fluoride deficiency., B. Ca deficiency., C. Vitamin K deficiency., D. Iron Deficiency
C: Vitamin K deficiency.
Answer: C: Vitamin K deficiency. 
Explanation: Vit K deficiency is associated with hemorrhagic disease of newborn which has manifested in this baby as Intracranial hemorrhage (bulging fontanel) and GI bleed (blood per rectum). Moreover home delivery (Vit K may not have been given at bih) and exclusive breast feeding (Vit K is deficient in breast milk) clearly point to Vit K deficiency as etiology.