3. (2 points) Consider an instruction within a certain instruction-set architecture (ISA): SUB R1, M2, R3. This instruction subtracts the contents of the virtual memory address M2 from the value in Register R1, and stores the result in Register R3. What is the maximum number of physical memory accesses that may be caused by this single instruction?

a) 1 b) 2 c) 3 d) 4