Final answer:
The default visibility timeout for an Amazon SQS queue is 30 seconds. This timeout ensures that once a message is being processed, it's not received by other consumers unless it becomes visible again after the timeout period.
Step-by-step explanation:
The student asked what the default setting is for the visibility timeout of an Amazon SQS queue. The correct answer is A. 30 seconds. When a message is received from a queue by a consumer, SQS prevents other consumers from receiving the message by making it invisible. This invisibility period is known as the visibility timeout, and it ensures that the message being processed isn't received by another consumer. If the processing of the message is successful, the message gets deleted, avoiding reprocessing. However, if the message is not processed within the visibility timeout period, it becomes visible again and may be received by another consumer for processing. The default visibility timeout for a new SQS queue is 30 seconds, which can be adjusted according to application-specific requirements.