The correct answer is D. All the above.
A boning rod is a tool used to check the levels of the sewer inverts. It is a long, thin rod with a pointed end. The rod is inserted into the sewer pipe and the level is checked by looking at the mark on the rod that lines up with the sewer invert.
Manhole covers are made circular for the convenience of the cleaning staff. The circular shape allows the manhole cover to be easily lifted and replaced.
A manhole is classified as shallow manhole if its depth is less than 0.9 m. This is because shallow manholes are easier to access and clean than deeper manholes.
Here are some additional details about each option:
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