Cisco Express Forwarding （CEF） is mainly used to increase packet switching speed， reducing theoverhead and delays introduced by other routing techniques， increasing overall performance.Which of the following concerning CEF is recommended by Cisco？（）
A、 Use default Layer 4 hash in core.
B、 Use default Layer 3 hash in distribution.
C、 Use default Layer 4 hash in distribution.
D、 Use default Layer 3 hash in core and Layer 3 + Layer 4 hash in distribution layer.
