A Solutions Architect is working with a company that operates a standard three-tier web application in AWS. The web and application tiers run on Amazon EC2 and the database tier runs on Amazon RDS. The company is redesigning the web and application tiers to use Amazon API Gateway and AWS Lambda, and the company intends to deploy the new application within 6 months. The IT Manager has asked the Solutions Architect to reduce costs in the interim.
Which solution will be MOST cost effective while maintaining reliability?

A. Use Spot Instances for the web tier, On-Demand Instances for the application tier, and Reserved Instances for the database tier.
B. Use On-Demand Instances for the web and application tiers, and Reserved Instances for the database tier.
C. Use Spot Instances for the web and application tiers, and Reserved Instances for the database tier.
D. Use Reserved Instances for the web, application, and database tiers.