Final answer:
The correct command for displaying the current directory is c) pwd, which stands for 'print working directory'.
Step-by-step explanation:
The command that would display the current directory you are in when entered at the root command prompt is c) pwd. The pwd command stands for 'print working directory' and it outputs the absolute path of the current working directory to the screen. This is a fundamental command in UNIX and UNIX-like operating systems, including Linux and MacOS.
The other commands listed have different functions: a) ls -l lists files in the current directory in a long format; b) cd .. changes the directory to the parent directory; d) cat file.txt displays the contents of a file called file.txt.