Answer:
The coastal regions and river valleys are the places where the populations are mostly concentrated.
Explanation:
The first option is not correct because the mountainous regions are generally avoided by the people, and the populations are usually (with exceptions around the Equator) small and sparse.
The second option is correct because the coastal regions enable the people to be very mobile, connected with other people through the water, have an abundance of food at disposal, and the climate is more pleasant.
The third option is correct because the river valleys, especially the ones where larger rivers pass through, have always been attractive for the people because of the abundance of freshwater, an abundance of fertile soil, and being able to use the rivers for traveling and trade.
The fourth option is not correct because the deserts are places that don't provide good living conditions, and often lack any conditions for that matter, so the people don't settle in them in large numbers.
