Which of the following rivers form the 'Sunderban Delta' ?

A river delta is a landform created where a river (or the combined flow of several rivers) deposits vast quantities of sediment as it meets a standing body of water such as a sea or bay; the world's largest deltas form where major river systems converge near their mouths.

The Ganga and the Brahmaputra converge in Bangladesh before draining into the Bay of Bengal. Their combined discharge carries an enormous silt load, which is deposited at the river mouth to build the Sunderban Delta (also called the Ganga–Brahmaputra Delta) — the largest delta in the world and home to the Sundarbans mangrove forest.

• Narmada and Tapi flow westward into the Arabian Sea through the Gulf of Khambhat; their estuaries do not build up sediment the way east-flowing rivers do, so they form estuaries, not a delta.

• Mahanadi and Godavari each build their own separate deltas on the eastern coast, well south of the Sunderban region.

• Krishna and Kaveri likewise form their own independent deltas further south on the south-eastern coast, unrelated to the Bengal delta system.

Hence, the Sunderban Delta is formed by the Ganga and the Brahmaputra.