QoS refers to the ability of a network to provide improved service， over various underlying technologies， to select network traffic. Which two traits are inherent to QoS？（）

• A、 reference to network ability to provide improved service to all network traffic
• B、 reduction in delay， jitter， and packet loss
• C、 equal handling of all packets
• D、 support for real-time applications
• E、 best-effort actions