The correct answer is Host hypervisor and virtualization layer.

The Host hypervisor and virtualization layer are part of the physical infrastructure that the cloud vendor controls across IaaS PaaS and SaaS. The vendor owns the physical hosts and the hypervisor that runs virtual machines and enforces tenant isolation, and those responsibilities do not shift to the customer in any service model.

Virtual networking and routing is not correct because networking responsibility can vary by model. In some models the provider manages the underlying physical network but customers often configure and manage virtual networks, routing tables, and security rules especially in IaaS.

Managed database services is not correct because that is a platform level service that the vendor provides in PaaS or managed service offerings, but customers can run and manage their own databases in IaaS, so responsibility is not always retained by the vendor.

Persistent block and object storage is not correct because while the vendor supplies and maintains the storage hardware, customers are responsible for the data, its configuration, and often encryption or backup choices depending on the service model.

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