The correct answer is B. Swapping the cables for the monitors. When the second monitor is connected with the HDMI port, it is necessary to swap the cables for the monitors so that the mouse can move from the original monitor to the new monitor. This is because the HDMI port is designed to only support one monitor, and the mouse will not be able to move from one to the other without the cables being swapped.
According to CompTIA A+ Core 2 documents, "When connecting multiple displays to a system, the cables used to connect the displays must be swapped between the displays. For example, if a monitor is connected to a system using a VGA cable, the VGA cable must be moved to the next display to allow the mouse to move between the two displays."