onsider the following memory reference string. What will be the number of page faults in case FIFO page eplacement algorithm is used and 4 physical memory frames are allocated for the process? reference String: 10120 3 0 4 2 3 0 3 21 2017013 O a. 12 b. 17 O c. 21 O d. 15 e. None of the above