Which type of Amazon EC2 instances should be used to reduce the cost of the system?

A solutions architect is designing a system to analyze the performance of financial markets while the markets are closed. The system will run a series of compute-intensive jobs for 4 hours every night. The time to complete the compute jobs is expected to remain constant, and jobs cannot be interrupted once started. Once completed, the system is expected to run for a minimum of 1 year.

Which type of Amazon EC2 instances should be used to reduce the cost of the system?
A . Spot instances
B . On-Demand instances
C . Standard Reserved Instances
D . Scheduled Reserved Instances

Answer: D