Why Correct: The Ganga-Brahmaputra delta forms where these rivers meet the Bay of Bengal through a funnel-shaped estuary, creating the world's largest estuarine delta.
Distractor Analysis: The Rhine delta in the Netherlands is an arcuate delta. The Mississippi delta in the Gulf of Mexico is a bird's foot delta. The Volga delta in the Caspian Sea is Europe's largest inland delta.
Takeaway: The Sundarbans mangrove forest occupies the Ganga delta, making it both an estuarine delta and the world's largest mangrove ecosystem.