This option is the most efficient because it uses API usage plans and API keys, which are features of Amazon API Gateway that allow you to control who can access your API and how much and how fast they can access it1. It also implements API usage plans and API keys to limit the access of users who do not have a subscription, which enables you to create different tiers ofaccess for your API and charge users accordingly. This solution meets the requirement of updating the application so that only users who have a subscription can access premium content. Option A is less efficient because it uses API caching and throttling on the API Gateway API, which are features of Amazon API Gateway that allow you to improve the performance and availability of your API and protect your backend systems from traffic spikes2. However, this does not provide a way to limit the access of users who do not have a subscription. Option B is less efficient because it uses AWS WAF on the API Gateway API, which is a web application firewall service that helps protect your web applications or APIs against common web exploits that may affect availability, compromise security, or consume excessive resources3. However,this does not provide a way to limit the access of users who do not have a subscription. Option C is less efficient because it uses fine-grained IAM permissions to the premium content in the DynamoDB table, which are permissions that allow you to control access to specific items or attributes within a table4. However, this does not provide a way to limit the access of users who do not have a subscription at the API level.