The correct answer is B because the object lifecycle in Cloud Storage can be automatically managed using a JSON document that defines the rules. This method is more efficient and less cumbersome than manually listing and deleting objects. Refer to the GCP documentation for gsutil lifecycle for more details. Option A is incorrect because XML is not supported by the gsutil command for lifecycle configurations. Options C and D are inefficient as they involve manually listing objects, calculating their age, and then deleting them, which is not optimal for ongoing cost management.