Which of the following is the main reason for the development of a dense air network in the Eastern U.S.A?

Industrialisation and Urbanisation with high standard of living

The correct answer is Option (4) → Industrialisation and Urbanisation with high standard of living

The Eastern U.S.A. has a dense population, well-developed industries, and numerous urban centers with a high standard of living. These factors generate high demand for frequent and efficient air travel, leading to the development of a dense air transport network.