Explanation:

- The Sundarbans Delta is a large coastal delta in the Bay of Bengal.

- It's formed by the confluence of several rivers.

- The delta is primarily created by the sediment deposition from the Ganga and Brahmaputra rivers.

- These rivers originate in the Himalayas and bring rich alluvial soil to the delta.

- The correct answer is Option 4: Ganga-Brahmaputra.

- Option 1: Sindhu-Brahmaputra - This combination doesn't form any known major delta.

- Option 2: Ganga-Sindhu - These rivers don't converge to create a delta. They flow into different areas.

- Option 3: Godavari-Krishna - These form deltas in southern India, but not the Sundarbans.