Consider a demand-paging system in which a process is allocated three frames. Let the Least Recently Used (LRU) page-replacement algorithm be used in the system. Let the sequence of page references for the process be as follows: 1, 3, 4, 1, 5, 2, 3, 1, 6, 2, 4, 3, 2, 4, 1, 6, 5, 6, 1, 5, 3, 1, 2, 4, 1, 2When processing each of the above page references, determine the set of pages resident in memory. Now, identify a triple from the following that represents a set of pages of the process that do not reside together in memory at the same time?a) {1, 2, 6} b) {2, 3, 4} c) {1, 4, 5} d) {3, 4, 5}