Which command is used to terminate a process?

Answer: Option D

In Unix, the kill command is used to terminate or send signals to processes. By default, it sends the TERM signal to a process, which instructs it to gracefully terminate. However, you can specify different signals using various options of the kill command. For instance, using kill -9 sends the KILL signal, which immediately terminates the process without allowing it to clean up.
So, Option D is the command used to terminate a process in Unix.