This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine System, Subject name: Physiology
Exposure to ultraviolet light directly facilitates which of the following? 
Select and explain. 
A. Conversion of 7 dehydrocholesterol to 25-hydroxycholecalciferol, B. Conversion of 25-hydroxycholecalciferol to 1,25- dihydroxycholecalciferol, C. Transpo of calcium into the extracellular fluid, D. Formation of calcium-binding protein
A: Conversion of 7 dehydrocholesterol to 25-hydroxycholecalciferol
Answer: A: Conversion of 7 dehydrocholesterol to 25-hydroxycholecalciferol 
Explanation: Ultraviolet light absorbed by the skin directly facilitates conversion of cholesterol to 25-hydroxycholecalciferol.