Q37

Consider a demand paging system with three frames, and the following page reference string: 1 2 3 4 5 4 1 6 4 5 1 3 2 . The contents of the frames are as follows initially and after each reference (from left to right):

$$\begin{array}{|c|lllllllllllll|} \hline \text{initially} & \text{after} \\ \hline -&1^* &2^* & 3^* & 4^* & 5^* & 4 & 1 & 6^* & 4 & 5 & 1^* & 3^* & 2^* \\ \hline -&1 & 1 & 1 & 1 & 1 & 1 & 1 & 6 & 6 & 6 & 6 & 6 & 2 \\ \hline -&- & 2 & 2 & 4 & 4 & 4 & 4 & 4 & 4 & 4 & 1 & 1 & 1 \\ \hline -&- & - & 3 & 3 & 5 & 5 & 5 & 5 & 5 & 5 & 5 & 3 & 3 \\\hline \end{array}$$

The *-marked references cause page replacements. Which one or more of the following could be the page replacement policy/policies in use?