单项选择题 A network administrator is verifying the configuration of a newly installed host by establishing an FTP connection to a remote server. What is the highest layer of the protocol stack that the nework administrator is using for this operation?（）

单项选择题 Refer to the exhibit, Host A pings interface S0/0 on router 3, what is the TTL value for that ping?（）

单项选择题 Which layer in the OSI reference model is responsible for determining the availability of the receiving program and checking to see if enough resources exist for that communication?（）