The correct answer is A. This solution uses AWS Lambda with SQS standard queues, which is more cost-effective than FIFO queues. It also employs AWS Key Management Service (KMS) for encryption, ensuring security. Moreover, it includes the kms:Decrypt permission for the Lambda execution role, fulfilling the requirement for each request to be processed at least once. This combination provides a secure, reliable, and cost-effective approach for handling asynchronous credit card validation requests.