An airline flight of 5 hours in the middle latitudes at an altitude of 12 km may result in an exposure of _____  µSv.: (A) 25, (B) 50, (C) 250, (D) 100
Answer is A. 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