Pick up the correct statement from the following :

ANS:E - All the above.

1. The boning rod is used for checking the levels of the sewer inverts: The boning rod is actually a construction tool used to check and set levels in various construction projects, including sewer construction. It's a long rod typically made of wood or metal, and it's used to ensure that surfaces, such as sewer inverts (the lowest part of a pipe's interior), are level or at the desired slope during construction. So, this statement is accurate.
2. Manhole covers are made circular for the convenience of the cleaning staff: While circular manhole covers do provide some convenience in terms of rolling the cover to access the manhole, the primary reason for their circular shape is structural. Circular shapes are inherently stronger and better distribute weight compared to other shapes like squares or rectangles. This design prevents the cover from falling into the manhole and ensures safety for pedestrians and vehicles. So, this statement is not entirely accurate.
3. A manhole is classified as a deep manhole if its depth is more than 1.5 meters: The classification of manholes as "deep" or "shallow" can vary based on local regulations and standards. While some guidelines may indeed classify manholes with a depth exceeding 1.5 meters as deep manholes, this threshold can vary. It's not universally defined as "more than 1.5 meters." So, this statement is somewhat accurate but lacks precision.
4. A manhole is classified as a shallow manhole if its depth is less than 0.9 meters: Similar to the previous statement, classifications of manholes can vary. Some standards may indeed classify manholes with depths less than 0.9 meters as shallow manholes, but again, this threshold can vary depending on local regulations and standards. So, this statement is somewhat accurate but also lacks precision.