A significant infrastructure project in Sikkim that is boosting connectivity is the:

Nathu La Pass
Sevoke-Rangpo railway line
Teesta River dam project
Sikkim International Airport

The correct answer is: d) Sikkim International Airport

Sikkim International Airport is a new airport under construction in Pakyong, Sikkim, India. It is expected to be completed in 2022 and will be the first international airport in the state of Sikkim. The airport will be a major boost to connectivity in the region and will help to promote tourism and economic development in Sikkim.

The other options are incorrect because:

  • Nathu La Pass is a high-altitude mountain pass in the Himalayas that connects India and China. It is a major trade route between the two countries, but it is not a significant infrastructure project in Sikkim.
  • Sevoke-Rangpo railway line is a railway line that connects Sevoke in West Bengal to Rangpo in Sikkim. It is a major railway line in the region, but it is not a significant infrastructure project in Sikkim.
  • Teesta River dam project is a hydroelectric dam project that is being constructed on the Teesta River in Sikkim. It is a major infrastructure project in Sikkim, but it is not a significant project that is boosting connectivity.