The correct answer is: a) India and China (Tibet).
The McMahon Line is a 2,414-kilometre (1,500 mi) border between India and China (Tibet). It was demarcated in 1914 by the Simla Convention between British India and Tibet. The line runs from the trijunction of India, China, and Bhutan in the west to the trijunction of India, China, and Myanmar in the east.
The McMahon Line was not accepted by China, and the border between India and China in the eastern sector remains disputed. The dispute over the McMahon Line has been a major source of tension between India and China since the 1950s.
Option b) is incorrect because the McMahon Line does not demarcate the border between India and Bhutan. The border between India and Bhutan is defined by the Indo-Bhutan Treaty of 1949.
Option c) is incorrect because the McMahon Line does not demarcate the border between India and Burma (Myanmar). The border between India and Burma (Myanmar) is defined by the Indo-Burma Boundary Agreement of 1960.
Option d) is incorrect because the McMahon Line does not demarcate the border between India and Nepal. The border between India and Nepal is defined by the Indo-Nepal Treaty of Peace and Friendship of 1950.