Which two statements about QoS options in a Cisco UCS environment are true？（）

A. The QoS policy assigns a system class to the outgoing traffic for a vNIC or vHBA.
B. Flow-control policies determine whether the uplink Ethernet ports in a Cisco UCS environment send and receive IEEE 802.3x pause frames when the send buffer for a port fills.
C. If no system class is configured as CoS 0， the Fibre Channel system class is used.
D. The user can configure QoS for these system classes： platinum， gold， silver， best effort， Fibre Channel.
E. When configuring a system class， the type of adapter in a server may limit the maximum MTU supported.