A company is planning to host an application that will be installed on a set of EC2 Instances. The application is a batch processing system. The system will be run on weekdays at certain times or even on the weekends. These batch processing workloads basically process data that business Intelligence applications will consume then. Which of the following is the most cost-effective option for the underlying instance provided an occasional interruption in the batch processing bearable?

Answer options:

A.Spot Instances
B.Reserved Instances
C.Dedicated Hosts
D.Dedicated Instances

Correct Answer: A
The AWS Documentation mentions the following.
A Spot Instance is an unused EC2 instance that is available for less than the On-Demand price. Because Spot Instances enable you to request unused EC2 instances at steep discounts, you can significantly lower your Amazon EC2 costs. The hourly price for a Spot Instance is called a Spot price. The Spot price of each instance type in each Availability Zone is set by Amazon EC2, and adjusted gradually based on the long-term supply of and demand for Spot Instances. Your Spot Instance runs whenever capacity is available, and the maximum price per hour for your request exceeds the Spot price.
Spot Instances are a cost-effective choice if you can be flexible about when your applications run and if your applications can be interrupted. For example, Spot Instances are well-suited for data analysis, batch jobs, background processing, and optional tasks. 
The other types of instances would not be cost-effective in this situation.
For more information on spot instances, please refer to the below URL-
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-spot-instances.html