A.Enable BPD guard
B.Disable CDP on ports where it is not necessary
C.Place unused ports in a common unrouted VLAN
D.Prevent automatic trunk configuration
E.Implement port security

A.BPDU guard can be used to prevent invalid BPDUs from propagating throughout the network. 
B.BPDU guard can guarantee proper selection of the root bridge.
C.BPDU guard can be utilized to prevent the switch from transmitteing BPDUs and incorrectly altering the root bridge election.
D.BPDU guard can be utilized along with PortFast to shut down ports when a switch is connected to the port.
E.None of the other alternatives apply