Which of the following Linux commands lists open files and what processes are using them?

The Linux command that lists open files and the processes that are using them is lsof. Here's how you can use it:

1. Open your terminal.
2. Type lsof and press Enter. This will list all the open files along with the processes that are using them.
3. If you want to find the files opened by a specific process, you can use lsof -p [PID], replacing [PID] with the process ID.
4. If you want to find the processes that have a specific file open, you can use lsof [file-name], replacing [file-name] with the name of the file.

Remember, you might need to have superuser (root) or sudo privileges to get information about files opened by other users' processes.