You enter configuration mode with the configure command. You need to abort the changes that you have made and start again with a fresh copy of the active configuration. Which command should you use?（）

A.save configuration <filename>
B.save config <filename>
C.save <filename>
D.save run <filename>

A.router’s version and serial number to help open a case with JTAC
B.software documentation describing features and configuration tasks within JUNOS
C.a brief description of commands and their default values
D.a verification of the current configuration on the router

A.space bar for both command and variable completion
B.space bar for command completion；tab key for variable completion
C.space bar for variable completion；tab key for command completion
D.tab key for variable and command completion；space bar for command completion