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.