->> Explain your heuristic for deciding whether a page fault for an
->> invalid virtual address should cause the stack to be extended into the
->> page that faulted.
+>> B3: When a process P obtains a frame that was previously used by a
+>> process Q, how do you adjust the page table (and any other data
+>> structures) to reflect the frame Q no longer has?
+
+>> B4: Explain your heuristic for deciding whether a page fault for an
+>> invalid virtual address should cause the stack to be extended into
+>> the page that faulted.