单项选择题 An operator needs to create /dir1/dir2/dir3. The /dir1 does not exist. What command can be used to create dir2 and dir3?（）

单项选择题 How can an operator list all its history of commands in one step?（）

单项选择题 An operator is asked to shutdown the telnet service for security reasons. What are the appropriate commands to achieve this?（）