Which of the following protocols utilize UDP as the layer 4 transport mechanism?（）

A.TFTP
B.SMTP
C.SNMP
D.FTP
E.HTTP
F.HTTPS

A. It is a route to be used when the routing protocol fails.
B. It is a route configured by an ISP that sends traffic into a corporate network.
C. It is a route used when a packet is destined for a remote network that is not listed in the routing table.
D. It is a route manually configured for a specific remote network for which a routing protocol is not configured.
E. It is used to send traffic to a stub network.

A. They establish routes that will never go down.
B. The keep routing tables small.
C. They require a great deal of CPU power.
D. The allow connectivity to remote networks that are not in the routing table.
E. They direct traffic from the Internet into corporate networks.