Correct choice is (b) Spoil Banks
For explanation I would say: The disposition of earth becomes costlier when the earthwork in excavation exceeds earthwork in filling. To dispose this earth economically, it should be collected on the edge of the bank embankment. The soil is deposited on both banks or only on one bank in the form of heaps. Longitudinal drains are excavated to run along their sides to dispose rain water.