A security architect is designing a Zero Trust architecture for an AI pipeline that processes sensitive healthcare data. The AI models must be trained in a network-isolated environment where no internet access is permitted. Which Azure Machine Learning network configuration provides a fully isolated training environment with no public internet connectivity?

B is correct because Azure Machine Learning managed virtual networks in 'Allow only approved outbound' mode restrict all outbound traffic from training compute to only explicitly approved destinations (such as Azure storage private endpoints and required Azure service endpoints). Disabling all outbound internet rules creates a fully isolated training environment where compute nodes have no internet access. A is incorrect because a customer-managed VNet with no internet gateway achieves isolation but requires more complex customer management of VNet routing and private endpoints; the AML managed VNet in 'Allow only approved outbound' mode provides the same isolation with Microsoft-managed network infrastructure. C is incorrect because NSG rules on the compute subnet can block outbound internet but do not provide the same management simplicity as the AML managed VNet and may still allow traffic that bypasses NSG through service endpoints. D is incorrect because subscription-level restrictions and no public IPs provide organizational-level controls but do not specifically configure the Azure Machine Learning workspace network isolation mode.