A company maintains a stateless web application that is experiencing inconsistent traffic. The company uses AWS CloudFormation to deploy the application. The application runs on Amazon EC2 On-Demand Instances behind an Application Load Balancer (ALB). The instances run across multiple Availability Zones.
The company wants to include the use of Spot Instances while continuing to use a small number of On-Demand Instances to ensure that the application remains highly available.
What is the MOST cost-effective solution that meets these requirements?

A. Add a Spot block resource to the AWS CloudFormation template. Use the diversified allocation strategy with step scaling behind the ALB.
B. Add a Spot block resource to the AWS CloudFormation template. Use the lowest-price allocation strategy with target tracking scaling behind the ALB.
C. Add a Spot Fleet resource to the AWS CloudFormation template. Use the capacity-optimized allocation strategy with step scaling behind the ALB.
D. Add a Spot Fleet resource to the AWS CloudFormation template. Use the diversified allocation strategy with scheduled scaling behind the ALB.