Which of the following are true about commands and files in Unix/Linux? Select one or more: a. A plain text file does not need to have the .txt extension to be able to be properly read from, and/or written to, by the operating system. b. The output of any executed command can either be printed out on-screen, written to a file, or serve as the input of another command/program. c. When a user wishes to read a text file, the user will always be able to read from that file as long as a valid path is provided. d. Given any three arbitrary commands x, y, and z that can be run from the Linux command line, the respective output from running these two command lines x; y; z; and x && y && z; are always equivalent. Which of the following are true about C programs? Select one or more: O a. When an executable C program terminates without printing any output whatsoever, it is impossible to determine if it has finished its task successfully, or encountered an error. b. When a C program whose source code is defined in a file named myprogram.cis compiled with the command gcc ./myprogram.c, it can then be executed by running the following command: ./myprogram c. The conversion of C source code into an executable involves pre-processing, compiling and linking. d. All C programs must be compiled before they can be executed