Consider the following memory reference string. What will be the number of page faults in case FIFO page replacement algorithm is used and 4 physical memory frames are allocated for the process?

Reference String: 1 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1 3

a. 12

b. 17

c. 21

d. 15

e. None of the above