单项选择题 The local host on a small network is named Earth. There is also a remote host on the network named Saturn.  The system administrator of the network is in the /u/tmp directory of Earth， and starts an ftp to Saturn as root.  Which of the following sequence of commands issued from the local host， Earth， will：（）。 1.Change to the /u/new directory on Saturn.   2.Check to see if there is an a.out file on remote host Saturn. 3.Transfer a.out from Earth to Saturn.

单项选择题 Whichofthefollowingcablesisthemostsusceptibletophysicaldamagebyroughhandling？（）

单项选择题 Whichofthefollowingcommandsisusedtoobservethecurrentstateoftheroutingtable？（）