The hilly terrain of Nagaland necessitates the construction of:

Elevated highways
Tunnels
Suspension bridges
All of the above

The correct answer is: d) All of the above.

Nagaland is a state in northeastern India. It is one of the most mountainous states in India, with an average elevation of 1,500 meters (4,900 feet). The hilly terrain of Nagaland necessitates the construction of elevated highways, tunnels, and suspension bridges to connect different parts of the state.

Elevated highways are built on pillars above the ground to avoid the steep slopes and valleys. Tunnels are built through mountains to shorten the distance between two points. Suspension bridges are built across rivers and gorges to provide a safe and convenient way for people and vehicles to cross.

The construction of these infrastructure projects has been a major challenge due to the difficult terrain and the remote location of many parts of the state. However, these projects have been essential for the development of Nagaland and have improved the lives of the people of the state.

Elevated highways are a type of road that is built above the ground on pillars. They are often used in mountainous areas to avoid the steep slopes and valleys. Elevated highways can be very expensive to build, but they can also be very efficient. They can help to reduce traffic congestion and improve safety.

Tunnels are a type of underground passage that is used to connect two points. They are often used in mountainous areas to avoid the steep slopes and valleys. Tunnels can be very expensive to build, but they can also be very efficient. They can help to reduce travel time and improve safety.

Suspension bridges are a type of bridge that is supported by cables that are suspended from towers. They are often used in mountainous areas to cross rivers and gorges. Suspension bridges can be very expensive to build, but they can also be very beautiful. They can help to improve the connectivity of different parts of a region.