Which physical security control BEST prevents an attacker from reading confidential data displayed on a monitor in an open-plan office where passersby can see the screen?

Why B is correct

A privacy screen filter uses micro-louver technology to narrow the viewing angle to approximately ±30 degrees from center, making the display appear black to anyone viewing from the side. This is the direct technical control for shoulder surfing in open-office environments. A password-protected screen saver protects an unattended workstation but does nothing while the user is actively working and data is displayed. Facing the monitor toward a wall may help in some layouts but is an architectural/positional workaround, not a privacy control. Watermarks on documents don't prevent viewing - they only deter unauthorized copying. The privacy filter is the industry-standard answer for this exact scenario.