What role does the QX55's motion-activated liftgate serve?

The motion-activated liftgate of the QX55 is designed to provide hands-free access to the cargo area, making it easier for users to load and unload items, especially when their hands are full. This feature enhances convenience, allowing users to open the liftgate simply by using a foot motion under the rear bumper, without the need to physically press any buttons or handle the liftgate.

The other options do not accurately describe the primary function of the motion-activated liftgate. While fuel efficiency and features related to automatic closing and vehicle alerts are important in other contexts, they do not pertain to the hands-free function of the liftgate itself. Thus, the correct answer emphasizes the practical benefit of accessing the cargo area easily and efficiently.