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 values of tear film break up time range from: 
Select and explain. 
A. 5 to 10 seconds, B. 10 to 15 seconds, C. 15 to 20 seconds, D. 15 to 30 seconds
D: 15 to 30 seconds
Answer: D: 15 to 30 seconds 
Explanation: Ans. 15 to 30 seconds