A.It may allocate IP addresses from an unknown subnet to the users.
B.All multicast traffic can be sniffed by using the DHCP multicast capabilities.
C.The CPU utilization of the first hop router can be overloaded by exploiting DHCP relay open ports.
D.A potential man-in-the-middle attack can be used against the clients.

A. 1） lowest root bridge id，2）lowest sender bridge id，3）lowest port id，4）lowest root path cost
B. 1） lowest root path cost，2）lowest root bridge id，3）lowest sender bridge id，4）lowest sender port id
C. 1） lowest root bridge id，2）lowest sender bridge id，3）lowest root path cost 4）owest sender port id
D. 1） lowest root bridge id，2）lowest root path cost，3）lowest sender bridge id，4）lowest sender port id