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
A stipulated flat sum the patient has to pay towards the cost of service before it goes into: 
Select and explain. 
A. Ground insurance, B. Co-insurance, C. Co-payment, D. Deductible
D: Deductible
Answer: D: Deductible 
Explanation: None