The correct answer is: The coastal regions.
The coastal regions have the highest population density because they are more fertile and have a more temperate climate than the other regions. The Imphal Valley is a hilly region with a tropical climate, and the hilly regions are also less fertile than the coastal regions. Remote border areas are sparsely populated because they are difficult to access and have a harsh climate.
The coastal regions are also home to many important ports and cities, which attract people from all over the country. The Imphal Valley is a major cultural and economic center, but it is not as well-connected to other parts of the country as the coastal regions. The hilly regions are home to many indigenous peoples, but they are not as well-developed as the coastal regions. Remote border areas are often neglected by the government, and they lack basic infrastructure and services.