(a) [3%] For a single-level page table, how much physical memory is needed for storing the page table?

(b) [3%] In a memory hierarchy system, we can integrate virtual memory, TLB and cache. A memory reference can encounter three different types of misses: a TLB miss, a page fault and a cache miss. Considering all the combinations of these three events with one or more occurring. Identify the number for the three events which is impossible.