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: Dental
Distance between x-ray source and film cassette should be: 
Select and explain. 
A. 60 inches, B. 50 inches, C. 65 Inches, D. 55 inches
C: 65 Inches
Answer: C: 65 Inches 
Explanation: 3 distances
x ray source – midsaggital  : 5 Feet : 60” : 152.4 cm
mid saggital – film cassettes  : 15 cm Acc to Jacobson
                                                          18 cm = 7” = Gurkeerat sing
x – ray source – film casetes : 176 ~ 170 cm
                around 66”