Answer is Round Robin (RR), option (B).
Now question is Why RR is most suitable for time shared OS?
First of all we are discussing about Time shared OS, so obviously We need to consider pre-emption .
So, FCFS and Elevator these 2 options removed first , remain SJF and RR from two remaining options.
Now in case of pre-emptive SJF which is also known as shortest remaining time first or SRTF (where we can predict the next burst time using exponential averaging ), SRTF would NOT be optimal than RR.
- There is no starvation in case of RR, since every process shares a time slice.
- But In case of SRTF, there can be a starvation , in worse case you may have the highest priority process, with a huge burst time have to wait.That means long process may have to wait indefinite time in case of SRTF.
That's why RR can be chosen over SRTF in case of time shared OS.