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.