The correct answer is D. All of the above.
Improper compaction of sub-grade is one of the main causes of depressions and undulations in the pavement. When the sub-grade is not properly compacted, it can settle over time, causing the pavement to sink. This can also happen if the sub-grade is not strong enough to support the weight of the pavement and the traffic that travels on it.
Impact of heavy wheel loads can also cause depressions and undulations in the pavement. When heavy vehicles drive over the pavement, they create a lot of force that can cause the pavement to crack and break. This can also happen if the pavement is not thick enough to withstand the weight of the vehicles.
Punching effect is another cause of depressions and undulations in the pavement. This happens when water seeps into the pavement and freezes, causing the pavement to expand and lift. This can also happen if the pavement is not properly sealed.
All of these factors can contribute to the formation of depressions and undulations in the pavement. It is important to identify the cause of the problem in order to properly repair it.