Step 1: Understanding the question.
The question asks about the structure most commonly used in India, which typically refers to administrative practices and systems.
Step 2: Evaluation of options.
- (A) Administrative: Correct. India uses administrative structures to organize its government and public services.
- (B) Medical: Incorrect. While medical structures are crucial, they are not the most commonly used in a general context.
- (C) Religious: Incorrect. Religious practices influence many aspects of society but are not the dominant structure.
- (D) International: Incorrect. International structures are not as regularly used within India compared to administrative systems.
Step 3: Conclusion.
Thus, the most regularly used structure is administrative.
Final Answer: Administrative.