The correct answer is A. AWS Cost and Usage Reports. This service provides detailed, hourly-level billing and usage data for your AWS account, allowing you to break down costs by service, tag, or custom dimensions. You can configure these reports to be delivered to an Amazon S3 bucket, which makes it easy to access and analyze your cost and usage data using various analytics and reporting tools. The other options do not meet the specific requirement of hourly detailed cost reports delivered to an S3 bucket. AWS Pricing Calculator is used to estimate costs, Cost Explorer provides interactive visualizations, and AWS Budgets helps you manage your AWS costs and usage.