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. It was drawn in 1914 by the British government and the Tibetan government, but China has never accepted it. The McMahon Line runs from the tripoint with Burma in the east to the tripoint with Nepal in the west. It separates the Indian state of Arunachal Pradesh from the Tibet Autonomous Region of China.
The McMahon Line was drawn in the Simla Convention of 1914, which was signed by the British government, the Tibetan government, and the Chinese government. The convention was intended to define the borders between British India, Tibet, and China. However, the Chinese government never ratified the convention, and it has never accepted the McMahon Line.
The McMahon Line became a contested border in 1962, when China invaded India. The Chinese army captured large parts of Arunachal Pradesh, but they withdrew after a few months. The border dispute between India and China remains unresolved.
Option b) India and Bhutan is incorrect because the border between India and Bhutan is defined by the Indo-Bhutanese Treaty of 1949.
Option c) India and Burma (Myanmar) is incorrect because the border between India and Burma is defined by the Indo-Burmese Boundary Agreement of 1960.
Option d) Assam and Arunachal Pradesh is incorrect because Assam and Arunachal Pradesh are both Indian states.