The correct answer is D. All of the above.
A water test is carried out to check the water tightness of the joints. This is done by filling the sewer line with water and then checking for any leaks. If there are any leaks, they will need to be repaired before the sewer line can be put into use.
A test for straightness is carried out with the help of a lamp and mirror. This is done by shining a light down the sewer line and then looking at the reflection in the mirror. If the sewer line is straight, the reflection will be a straight line. If the sewer line is not straight, the reflection will be a curved line.
An obstruction test is carried out with the help of a smooth ball of diameter 13 mm. This is done by dropping the ball down the sewer line and then listening for it to hit the bottom. If the ball hits the bottom, then the sewer line is clear. If the ball does not hit the bottom, then there is an obstruction in the sewer line that needs to be removed.
It is important to carry out all of these tests to ensure that the sewer line is in good working condition and will not cause any problems.