Which three statements are true about the application of QoS models？ （）

A. The DiffServ model requires applications to signal the network with QoS requirements.
B. The DiffServ model can be used to deliver QoS based upon IP precedence， or source and destination addresses.
C. The DiffServ model requires RSV
D. The best effort model is suitable for applications such as file transfer and e-mail
E. The IntServ model requires applications to signal the network with QoS requirements.
F. The IntServ model attempts to deliver a level of service based on the QoS specified by each packet