To meet the requirement with the least manual effort between environment deployments, the infrastructure engineers should focus on solutions that automate and standardize the deployment process across multiple environments, Regions, and accounts. Option A suggests using AWS CloudFormation parameters for values that vary across environments and Regions, which allows for dynamic input and reduces manual configuration. This approach ensures consistency and reusability of the CDK application. Option C proposes creating a dedicated account for shared application services and deploying a CDK pipeline to this account. This pipeline can then deploy the CDK application across different environments and Regions, automating the deployment process and ensuring consistency. This method leverages AWS best practices for multi-account and multi-Region deployments, making it an efficient solution. Options B, D, and E either require manual intervention, lack scalability, or do not fully leverage AWS services for automation and consistency, making them less optimal choices.