Why Does the Population of Nauru Cluster Together in Quasi-Urban

Why does the population of Nauru cluster together in quasi-urban settings?

A) It is a cultural tradition for them to live in close quarters.
B) The brown tree snake population is so large and dangerous that the island's inhabitants must live in large, fenced, snake-proof compounds.
C) Phosphate mining on the island has left limited room for habitation.
D) They are at war with the Solomon Islands and must live in fortified compounds.
E) The settlements are located at the few sources of water on the island.