The longest border between any two countries in the world is between :

1. A. (a) Canada and the United States of America
2. B. (b) Chile and Argentina
3. C. (c) China and India
4. D. (d) Kazakhstan and Russian Federation

Answer: A

Explanation

This is a factual question about international borders. The longest international border between any two countries in the world is indeed shared by Canada and the United States of America. This border stretches approximately 8,891 kilometers (5,525 miles), including the Alaska-Canada border. While other options represent significant borders, none are as long as the Canada-US border. For instance, the Russia-Kazakhstan border is about 7,644 km, and the Chile-Argentina border is about 5,308 km. The India-China border is approximately 3,488 km. Knowledge of world geography, including physical and political features, is a standard part of the UPSC Geography syllabus. This type of question tests basic geographical facts.