The Nathu La Pass, a high-altitude mountain pass on the border with China, is:

The correct answer is: b) Only accessible by special permits.

Nathu La Pass is a high-altitude mountain pass on the border between India and China. It is located in the Himalayas, at an elevation of 4,310 meters (14,140 feet). The pass was opened to trade and tourism in 1992, but it is only accessible by special permits. The permits are issued by the Indian government and are required for all Indian and foreign nationals. The pass is closed from December to April due to heavy snowfall.

Option a) is incorrect because the Nathu La Pass is not open year-round for public transportation. It is only accessible by special permits.

Option b) is correct because the Nathu La Pass is only accessible by special permits. The permits are issued by the Indian government and are required for all Indian and foreign nationals.

Option c) is incorrect because the Nathu La Pass is currently used for transportation. It is open to trade and tourism.

Option d) is incorrect because the Nathu La Pass is not primarily used for military purposes. It is used for trade and tourism.