The correct answer is B, AWS Lambda. AWS Lambda is a serverless compute service that allows you to run code without provisioning or managing servers. It is designed to handle applications with short runtimes and is event-driven, which means it can automatically respond to changes in data or system state. This service is cost-effective as you only pay for the compute time you consume, measured per millisecond, without the need to provision infrastructure upfront for peak capacity. This meets the company's requirements for maximizing operational efficiency and minimizing costs.