A system engineer designs a CPU scheduler using MLFQ algorithm. After testing, he found that some processes can maintain their high priority by periodically giving up CPU before their time slice ends. This cause the low$-$level processes starved. What adjustment does he need to fix this problem?

a$.$

Adding this rule: after some period of time, move all the jobs to the topmost queue.

b$.$

dropping this rule: if a job gives up CPU before time slice is up$,$ keep it at the same priority level.

c$.$

Adding this rule: once a job uses up its total assigned time allotment at a given priority level, demote its priority to the next level.

d$.$

Removing this rule: If job A has the same priority level as job B$,$ running these jobs in round robin mode.