You are developing an ecommerce web application that uses App Engine standard environment and Memorystore for Redis. When a user logs into the app, the application caches the user's information (e.g., session, name, address, preferences), which is stored for quick retrieval during checkout.
While testing your application in a browser, you get a 502 Bad Gateway error. You have determined that the application is not connecting to Memorystore. What is the reason for this error?

A. Your Memorystore for Redis instance was deployed without a public IP address. B. You configured your Serverless VPC Access connector in a different region than your App Engine instance. C. The firewall rule allowing a connection between App Engine and Memorystore was removed during an infrastructure update by the DevOps team. D. You configured your application to use a Serverless VPC Access connector on a different subnet in a different availability zone than your App Engine instance.