The correct answer is B. According to the AWS documentation and user feedback, a client can invalidate an API Gateway cache entry by sending a request with the Cache-Control:max-age=0 HTTP header. This header instructs the API Gateway to bypass the cache and reload the response from the integration endpoint. Attaching an InvalidateCache policy to the IAM role used by customers and instructing them to include this header in their requests ensures they have the necessary permissions and method to invalidate the cache.