ANS:D - all of these.

The correct answer is: all of these. Explanation:

1. Water Test: The water test is a common method used to test the integrity and tightness of sewer pipes. In this test, the sewer pipes are filled with water to a specific level, and the water level is monitored for any signs of leakage or seepage. The water test helps identify any defects or weaknesses in the sewer pipes that could lead to leaks or infiltration of groundwater.
2. Ball Test: The ball test, also known as the pipeline ball test, is another method used to test the integrity of sewer pipes. In this test, an inflatable ball or plug is inserted into the sewer pipe and inflated to block the flow of water. The pipe is then pressurized, and the pressure is monitored for any drops, which could indicate leaks or defects in the pipe.
3. Mirror Test: The mirror test is less common but may be used in certain situations to inspect the interior of sewer pipes for cracks, corrosion, or other defects. A mirror attached to a long pole or rod is inserted into the sewer pipe, allowing inspectors to visually examine the condition of the pipe walls and joints.

All of these tests serve the purpose of ensuring the quality, functionality, and structural integrity of sewer pipes before they are installed or put into service. Each test method has its advantages and limitations, and the choice of test may depend on factors such as the type of pipe, project specifications, and regulatory requirements.