Which of the following tools are used to measure memory usage? (Select THREE correct answers.)

`mpstat` (multiprocessor statistics) is primarily used for reporting processor-related statistics for individual CPUs or cores, not for detailed memory usage.

`pstree` displays running processes as a tree, showing process relationships, but it does not provide quantitative measurements of resource usage like memory.

`sar` (System Activity Reporter) collects, reports, and saves system activity information, including detailed memory statistics such as used memory, free memory, swap usage, and buffer/cache memory.

`top` provides a real-time, dynamic view of running processes, displaying their individual memory consumption (resident set size, virtual memory size) as well as overall system memory and swap usage.

`vmstat` (virtual memory statistics) reports comprehensive information about processes, memory (including free, buffer, cache, swap), paging activity, and CPU usage, making it excellent for assessing memory bottlenecks.