$17.$ Which command is called as the end$-$of$-$file command?a$)$ Ctri$+$ V b$)$ Cul$+$ Bc$)$ Ctrl$+$ D d$)$ Cult C$18.$ Which of the following is called as the piping symbol?b$)$Id$)!19.$ Which of the following command is used to sort the lines of data in a file in alphabeticala$)$ Sortb$)$ Shc$)$ Std$)$ Sort $-$r$20.$ In which of the following directory does the configuration files are present?a$)/$bin$/$b$)/$root$/$c$)/$etc$/$d$)/$dev$/$