Final answer:
The correct answer is a) Page table base register. It is used in a computer's virtual memory system to map virtual addresses to physical addresses.
Step-by-step explanation:
For larger page tables, they are kept in main memory and a page table base register points to the page table. The correct answer is a) Page table base register. This register is crucial for the operation of a computer's virtual memory system. It contains the base address of the page table, which is used by the memory management unit (MMU) to map virtual addresses to physical addresses when a program is executed.