Explanation:

- Program Counter (Option 3): This register holds the address of the next instruction that the CPU will execute. It automatically increments after each instruction is fetched, ensuring the CPU knows where to find the next instruction.

- Memory Address Register (Option 1): This register holds the memory location of data that needs to be accessed, either for reading or writing.

- Memory Buffer Register (Option 2): Used to temporarily hold data being transferred to or from memory.

- Memory Data Register (Option 4): Holds the actual data being read from or written to the memory locations.