Introduction:
The pile load test is a crucial test conducted in the field of civil engineering to determine the load-bearing capacity and the overall performance of a pile foundation. This test is performed on both working piles and test piles.

Explanation:
a) Working pile:
- A working pile refers to a pile that is part of the actual foundation system designed to support the structure.
- These piles are installed during the construction phase and are subjected to the actual loads from the structure.
- The primary purpose of a working pile is to provide support and stability to the structure.
- The pile load test is performed on working piles to assess their load-bearing capacity and ensure that they meet the design requirements.
- It helps to verify whether the working piles are capable of safely carrying the loads imposed by the structure.

b) Test pile:
- A test pile, on the other hand, is specifically installed for the purpose of conducting load tests.
- Test piles are typically installed adjacent to the working piles and are not part of the actual foundation system.
- These piles are used to evaluate the soil conditions, determine the load-bearing capacity, and assess the performance of the pile foundation.
- The test pile is subjected to a controlled load incrementally to measure the settlement response and load capacity of the pile.
- The data obtained from the test pile is used to validate the design assumptions and to optimize the pile foundation for the structure.

c) All of the mentioned:
- The pile load test is performed on both working piles and test piles.
- It is essential to conduct the test on working piles to ensure their load-bearing capacity and performance.
- Test piles provide valuable information about the soil conditions and help in optimizing the design of the pile foundation.
- Therefore, the pile load test should be performed on both working piles and test piles to ensure the overall safety and efficiency of the pile foundation system.

Conclusion:
In conclusion, the pile load test should be performed on both working piles and test piles. This comprehensive testing approach helps validate the design assumptions, optimize the foundation system, and ensure the overall performance and safety of the pile foundation.