The correct answer is B. Resource elasticity. This concept refers to the ability of cloud services to automatically scale resources up or down based on the demand of the application. It allows users to add or remove computing resources quickly to match their workload, ensuring efficient use of resources and cost-effectiveness. This is a key advantage of cloud computing and a fundamental aspect of the AWS platform, as it enables businesses to be agile and responsive to changes in demand without the need for significant upfront investment in infrastructure.