The correct answer is D. All the above.
A manhole is a structure that provides access to a sewer, drain, or other underground utility. It is typically cylindrical in shape and has a cover that can be opened to allow workers to enter and inspect the utility. Manholes are typically located at bends, junctions, and changes of gradient in the utility line. This is because these are the locations where there is a greater risk of blockages or other problems.
Bends in a utility line can cause sediment to build up, which can lead to blockages. Junctions are where two or more utility lines come together, and this can also be a location where blockages occur. Changes of gradient can cause the utility line to settle unevenly, which can also lead to problems.
By providing access to these locations, manholes allow workers to inspect the utility and make repairs as needed. This helps to prevent problems from occurring and keeps the utility in good working order.
In addition to the locations mentioned above, manholes are also typically located at the beginning and end of a utility line, as well as at any other location where access is needed for maintenance or repair.