Which statement is correct about the number of available QoS system classes in FCoE？（）

A、 It’s hard-set and cannot be disabled

B、 It’s configurable， with an upper limit of 16

C、 It’s hard-set but cannot disable best-effort and Fibre Channel

D、 It’s hard-set but can disable all but one class

E、 It’s configurable with an upper limit of eight