Generally We know that The Real Time Operating System jobs are highly associated with The Timings or Deadlines.So it is always preferable to use a Preemptive scheduling scheme.
Therefore we can eliminate B option as FCFS is a Non-preemptive scheduling scheme.
Option D is also not preferable because we should use only preemptive scheme.But Random scheduling means any Non preemptive or Preemptive.
Now Option A,Yes it is preemptive but still it’s not preferable as we will not have any priority oriented mechanisms in it…It slightly follows FCFS.
So,It is C..Preemptive scheduling scheme …
Apart from question i think Preemptive scheduling scheme based on priority is better.