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

A.RTP traffic is exchanged between IP phone P1 and IP phone P2. IP phone P1 alerts the CCM of off-hook state. CCM instructs IP phone P1 to provide dialtone. IP phone P1 passes digits to CCM. CCM routes call to PSTN or IP phone P2.
B.CCM instructs IP phone P1 to provide dialtone. IP phone P1 alerts the CCM of off-hook state. IP phone P1 passes digits to CCM. CCM routes call to PSTN or IP phone P2. RTP traffic is exchanged between IP phone P1 and IP phone P2. 
C.CCM instructs IP phone P1 to provide dialtone.IP phone P1 alerts the CCM of off-hook state. IP phone P1 passes digits to CCM. RTP traffic is exchanged between IP phone P1 and IP phone P2. CCM routes call to PSTN or IP phone P2.
D.IP phone P1 alerts the CCM of off-hook state. CCM instructs IP phone P1 to provide dialtone. IP phone P1 passes digits to CCM. CCM routes call to PSTN or IP phone P2. RTP traffic is exchanged between IP phone P1 and IP phone P2.