Which of the following is NOT a VLAN Trunking Protocol (VTP) mode of operation?

A.
client

B.
server

C.
virtual

D.
transparent

Explanation:
Virtual is not a valid VTP mode of operation. There are three different VTP modes of operation: client, server, and transparent.
In client mode, a switch can synchronize VLAN information with the domain and forward advertisements. However, VLANs cannot be created, deleted, or modified
from a switch in client mode. Also, a client mode switch does not save VLAN information in non-volatile Random Access Memory (NVRAM). It is stored in Flash in a
file called vlan.dat.
In server mode, a switch synchronizes the VLAN information with the domain, sends and forwards advertisements, and can create, delete, or modify VLANs. In
server mode, VLAN information is stored in Flash in a file called vlan.dat.
In transparent mode, a switch does not synchronize its VLAN configuration with the domain, but it forwards advertisements. VLANs can be created, deleted, or
modified locally and VLAN configuration is saved in both the running-config file in RAM and in flash in a file called vlan.dat.
Objective:
LAN Switching Fundamentals

Sub-Objective:
Configure, verify, and troubleshoot VLANs (normal range) spanning multiple switches

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/25sg/configuration/guide/conf/vlans.html