The formation of Sundarbans is explained by which combined river process?

Correct answer: Sediment deposition and distributary development by Ganga and Brahmaputra

The Sundarbans is a vast deltaic and mangrove region formed mainly by the Ganga and Brahmaputra river systems. These rivers carry sediment from the land and deposit it where their channels approach the Bay of Bengal. The channels divide repeatedly into distributaries, while tidal water, mudflats, and low-lying islands shape the landscape. Mangrove vegetation grows well in this muddy, saline, regularly flooded environment.

Option A correctly combines sediment deposition with the development of distributaries by the Ganga and Brahmaputra. The Narmada is associated with a rift valley, not the Sundarbans. The Luni belongs to the arid western region, and the Indus does not explain this eastern deltaic mangrove system. Therefore the supplied answer is correct, and the useful association is “Sundarbans—Ganga-Brahmaputra delta—mangroves.”