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
Efficacy of a new drug A is compared with an existing drug B in : 
Select and explain. 
A. Clinical trial phase I, B. Clinical trial phase II, C. Clinical trial phase III, D. Clinical trial phase IV
C: Clinical trial phase III
Answer: C: Clinical trial phase III 
Explanation: None