Final answer:
Typically, a CPU will complete the current disk-service routine before processing another I/O interrupt unless the new interrupt has a higher priority and the CPU supports preemption.
Step-by-step explanation:
When a CPU with interrupt-driven I/O is busy servicing a disk request and another I/O interrupt occurs, the behavior that follows depends on the CPU's interrupt handling and the priority of the interrupts. Normally, the CPU will complete the current disk-service routine before processing the second interrupt. This is because interrupts can typically be prioritized, and a service routine will not be interrupted by another interrupt of equal or lower priority.
In the case where the new interrupt has a higher priority, some CPUs can preempt the current service routine to service the higher-priority interrupt. However, without specific information on the priority settings or the ability to handle nested interrupts, the most likely scenario is d) Processing the second interrupt after finishing the current routine.