A company has an uninterruptible application that runs on Amazon EC$2$ instances. The application constantly processes a backlog of files in an Amazon Simple Queue Service $($Amazon SQS$)$ queue. This usage is expected to continue to grow for years. What is the MOST cost$-$effective EC$2$ instance purchasing model to meet these requirements? A$.$ Spot Instances B$.$ On$-$Demand Instances C$.$ Savings Plans D$.$ Dedicated Hosts