The correct answer is option 3 - Sikkim. Nathu La is a mountain pass that is located in the Indian state of Sikkim. A mountain pass is a route through a mountain range or over a ridge that allows travel between two regions. Nathu La is situated at an elevation of 4,310 meters (14,140 ft) above sea level and connects the Indian state of Sikkim with Tibet Autonomous Region in China. It is one of the three open trading border posts between India and China and is important for bilateral trade and cultural exchanges between the two countries. The pass is also of significant historical importance as it has been part of several military conflicts between India and China. It was closed in 1961 during the Sino-Indian War and was re-opened in 2006 for limited trade and travel. Nathu La provides stunning panoramic views of the surrounding Himalayan mountains and is a popular tourist destination in Sikkim.