Final answer:
When the sum of the working-set sizes exceeds the available frames, the operating system will typically suspend a process to manage resources efficiently and prevent system instability or excessive paging (thrashing).
Step-by-step explanation:
If the sum of the working-set sizes increases, exceeding the total number of available frames, the correct answer is that d) the operating system selects a process to suspend. This is part of the operating system's memory management strategy. When there isn't enough physical memory to hold all the working sets of all processes, the operating system must take measures to ensure that the system continues to operate efficiently.
The 'working set' is a term used in computing that refers to the set of pages or frames that a process is currently using. This concept is often used in the context of virtual memory systems. If the working sets of all processes grow larger than the physical memory, it could lead to excessive paging, also known as thrashing, where the system spends more time paging than executing processes. To mitigate this, the operating system may decide to suspend, or swap out, one or more processes to decrease the memory demand, thus keeping the system stable.