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: Ophthalmology
Normal value of tear film break-up time 
Select and explain. 
A. 5-10 seconds, B. 10-15 seconds, C. 15-30 seconds, D. > 35 seconds
C: 15-30 seconds
Answer: C: 15-30 seconds 
Explanation: Tear Film break-up time:
It is the interval between a complete blink and appearance of first randomly disributed dry spot on the cornea.
Normal value - 15-35 seconds.