On a Linux device, which of the following commands will start the Nessus client in the background so that the Nessus server can be configured?

The `+` character has no defined meaning as a background execution operator in Linux shell syntax and is not a valid Nessus CLI flag.

`*s` is not a valid shell operator or Nessus argument for background execution; the asterisk is a glob wildcard, not a process control symbol.

The `&` operator in Linux/Unix shells instructs the shell to fork the process and run it in the background, returning control to the terminal immediately. This allows the Nessus client to start and remain running so the administrator can then access and configure the Nessus server interface without blocking the current shell session.

The `-d` flag conventionally indicates debug or daemon mode depending on the application, but it is not the standard Linux shell mechanism for sending a process to the background.