Question

give reasons why plains and river valleys are most densely populated? ​

Answer 1

Answer:

Plains and river valleys are most densely populated because the river nearby provide water.The construction and development can be more in plains and river valleys

Answer 2

Answer:

Plains are flat

so we can build railway tracks build proper houses and an ample supply of minerals.

Rivers  provide water and supports their needs and fish to eat.

When the river floods, the land is fertile for farming.

That is why they are populated