is) Demand Paging Memory Allocation allows Memory Manager to solve problems of 18.1 internal fragmentation; 18.2 keeping large tables in the memory 18.3 having job size limited to physical memory size; 18.4 eliminating overhead for handling necessary paging hardware 18.5 eliminating possibility of thrashing. 19) If the Modified Bit in the Page Map Table equal to 1, it means: 19.1 the page must be modified 19.2 the page cannot be modified; 19.3 the page must be saved before removing it from the memory 19.4 an address of the page must be modified 19.5 the page may be relocated in the memory 20) The main disadvantage of First-Come First-Serve process scheduling algorithm is 20.1 the rank of turnaround time varies widely; 20.2 the turmaround time is always very big 20.3 the waiting time is always very big: 20.4 the algorithm is very complex in implementation 20.5 the algorithm can be used only for short jobs