Option D (Track client status with Amazon ElastiCache) is correct because using ElastiCache allows the backend service to efficiently track client connection status without querying a database, thereby detecting clients that frequently connect and disconnect. Option E (Implement $connect and$disconnect routes in the backend) is correct because $connect and$disconnect routes are reserved routes in WebSocket APIs, automatically triggered when a client connects or disconnects, enabling the backend service to manage the client's connection state.