Option A is correct because SageMaker AI Notebook Instances support Git repositories as SageMaker resources, and private repository credentials can be stored in AWS Secrets Manager. This satisfies the requirement with the least operational overhead because the notebook instances can remain isolated from direct internet access while SageMaker manages repository association and authentication. Placing credentials inside a URL is insecure and does not properly solve credential management. NAT gateway options introduce internet egress into the VPC, which conflicts with the isolation requirement and adds operational and security complexity. Network ACLs are not suitable for controlling access to a specific Git URL because they operate at the subnet and IP/port level, not at an application URL level. (AWS Documentation)

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