The correct answer is A. Spot Instances. They are a cost-effective option for running applications on Amazon EC2 for short periods of time, as they are available at a significant discount compared to On-Demand instances. The key feature of Spot Instances that makes them suitable for the scenario described is their ability to be interrupted by Amazon EC2 with a two-minute notification when the capacity is needed back. This characteristic aligns with the requirement that the applications can be interrupted. On-Demand Instances (B) do not offer the same cost savings and are not designed for applications that can be interrupted. Reserved Instances (C) require a commitment and are not as cost-effective for short-term runs. Dedicated Instances (D) are more expensive and are not intended for short-term, interruptible applications.