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: Pharmacology
Comparison of efficacy of a new drug B with an existing drug A is done in which phase of clinical trials ? 
Select and explain. 
A. Phase I, B. Phase II, C. Phase III, D. Phase IV
C: Phase III
Answer: C: Phase III 
Explanation: "The purpose of phase III trials is to obtain adequate data about the efficacy and safety of drugs in a larger number of patients of either sex in multiple centres usually in comparison with the standard drug."