The IP subsystem fallover behavior of a two-node cluster is being testing in a large client organization. One of the tests is to simulate a network_down event and verify that HACMP movesthe single resource group to the standby node. What is the best way to simulate a network down condition？（）

A. Turn off the IP core switch connecting the two nodes.
B. Issue the command "stopsrc -g inetd" on the node that has the resource group.
C. Issue the command "sh /etc/rc.tcpclean" on the node that has the resource group.
D. Simultaneously unplug all network cables from the node that has the resource group.