For a certain page trace starting with no page in the memory, a demand-paged memory system operated under the LRU replacement policy results in 9 and 11 page faults when the primary memory is of 6 and 4 pages, respectively. When the same page trace is operated under the optimal policy, the number of page faults may be:
(a) 9 and 7
(b) 7 and 9
(c) 10 and 12
(d) 6 and 7
