The correct answer is: D. All the above
A spoil bank is a mound of earth that is created when soil is excavated from a canal or other excavation. Spoil banks are typically used to provide stability to the canal banks and to prevent erosion. They can also be used to create wildlife habitat or to provide a place for people to walk or ride their bikes.
In some cases, spoil banks are created on both sides of a canal. This is often done when the canal is being constructed through a narrow valley. The spoil banks on either side of the canal can help to support the weight of the earth and prevent it from collapsing into the canal.
In other cases, spoil banks are only created on one side of a canal. This is often done when the canal is being constructed through a wider area. The spoil bank on one side of the canal can help to support the weight of the earth and prevent it from collapsing into the canal. It can also be used to create a barrier between the canal and the surrounding area.
The decision of whether to create a spoil bank on one side of the canal or on both sides of the canal is made by the engineer who is designing the canal. The engineer will consider the factors such as the width of the valley, the type of soil, and the amount of water that will be flowing through the canal.