正解:D
This is because a virtual switch is a software-based switch that operates at the data link layer of the OSI model and provides connectivity between virtual machines that are running on the same physical host or different hosts. A virtual switch can also connect virtual machines to external networks, such as the Internet or a local area network, by using physical network adapters on the host. A virtual switch can perform the same functions as a physical switch, such as learning MAC addresses, forwarding frames, and applying VLANs. The source of this answer is the Cisco ENCOR v1.1 course, module 9, lesson 9.1: Implementing Network Virtualization.