The correct answer is: C. Fields on both sides of the canal.
Borrow pits are excavation sites where soil is removed to be used for other purposes, such as construction. They should be located in fields on both sides of the canal to minimize the impact on the canal and to ensure that the soil is not removed from areas that are important for drainage or other purposes.
Option A is incorrect because it would only remove soil from one side of the canal, which could disrupt the flow of water and cause erosion. Option B is incorrect for the same reason. Option D is incorrect because it would remove soil from the central half width of the canal, which is the most important area for drainage.
In addition to minimizing the impact on the canal, it is also important to choose a location for a borrow pit that is safe and accessible. The pit should be located in an area that is not prone to flooding or landslides, and it should be accessible by road or by other means.