The correct answer is D. Program Counter.
The program counter (PC) is a register in a computer processor that indicates the address of the instruction that the processor is currently executing. The PC is incremented by one after each instruction is executed, so it always points to the next instruction that should be executed.
The memory address register (MAR) is a register in a computer processor that stores the address of the memory location that is currently being accessed. The MAR is used in conjunction with the memory data register (MDR) to read data from or write data to memory.
The instruction register (IR) is a register in a computer processor that stores the instruction that is currently being executed. The IR is used by the processor to decode the instruction and determine what actions to take.
The memory data register (MDR) is a register in a computer processor that stores data that is being read from or written to memory. The MDR is used in conjunction with the MAR to read data from or write data to memory.
Therefore, the only register that is loaded with the contents of the memory location pointed by the PC is the program counter (PC).