Which three statements are correct about the IEEE 802.3af Power over Ethernet standard? (Choose three)

A.
It defines a port that acts as a power source to be a PSE

B.
It defies a powered device to be a PDE

C.
It defies how a powered device is detected

D.
It defies three methods of delivering Power over Ethernet to the discovered powered device

E.
It describes five power classes to which a device may belong

F.
It defines power class 0 as being reserved for future use