The correct answer is C. Create rule sets in AWS CloudFormation Guard. Run validation checks for CloudFormation templates as a phase of the CI/CD process.

This answer is correct because AWS CloudFormation Guard is a tool that helps you implement policy-as-code for your CloudFormation templates. You can use Guard to write rules that define your security policies, such as requiring encryption for EBS volumes, and then validate your templates against those rules before deploying them.You can integrate Guard into your CI/CD pipeline as a step that runs the validation checks and prevents the deploymentof any non-compliant templates12.

The other options are incorrect because:

A. Turning on AWS Trusted Advisor and configuring security notifications as webhooks in the preferences section of the CI/CD pipeline is not a solution, because AWS Trusted Advisor is not a policy-as-code tool, but a service that provides recommendations to help you follow AWS best practices.Trusted Advisor does not allow you to define your own security policies or validate your CloudFormationtemplates against them3.

B. Turning on AWS Config and using the prebuilt or customized rules is not a solution, because AWS Config is not a policy-as-code tool, but a service that monitors and records the configuration changes of your AWS resources.AWS Config does not allow you to validate your CloudFormation templates before deploying them, but onlyevaluates the compliance of your resources after they are created4.

D. Creating rule sets as SCPs and integrating them as a part of validation control in a phase of the CI/CD process is not a solution, because SCPs are not policy-as-code tools, but policies that you can use to manage permissions in your AWS Organizations.SCPs do not allow you to validate your CloudFormation templates, but only restrict the actions that users and roles can perform in your accounts5.