Option D is the correct answer. Configuring a lifecycle management policy for the storage account allows you to automatically delete files that exceed the retention period, ensuring that the data retention policy is enforced. Option A is incorrect because moving files to a separate storage account does not enforce the retention policy. Option B is incorrect because it requires manual intervention and does not provide a real-time solution. Option C is incorrect because while Azure Event Grid can be used for event-driven scenarios, it does not provide a direct mechanism for enforcing data retention policies.