This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
An airline flight of 5 hours in the middle latitudes at an altitude of 12 km may result in an exposure of _____  µSv. 
Select and explain. 
A. 25, B. 50, C. 250, D. 100
A: 25
Answer: A: 25 
Explanation: Directly picked from White and Pharoah:
"An airline flight of 5 hours in the middle latitudes at an altitude of 12 km may result in an exposure of about 25 µSv".
White and Pharoah's Oral  Radiology Principles and Interpretation 8th edition