The indus valley are believed to have been settled: -after farms failed elsewhere and farmers migrated to the valley -when the river flooded its banks and left fertile silt in which to farm -when crops such as millet were found along the banks -when the people began worshipping multiple gods

The correct answer is - when crops such as millet were found along the banks.

The Indus Valley is a valley that has a very big river flowing through it, and also very fertile soil around its banks, but it wasn't until the discovering of the millet and its nutrition value that the valley has been used for farming. Once the people recognized the potential of the millet as a big and stable food source, they started to use the advantages of the fertile valley and develop the agriculture in this part of the world.