Which of the following is a sign that wheels may be out of alignment?

C is the correct choice as pulling to one side or having an off-center steering wheel distinctly indicates that the wheels may be out of alignment. When the alignment of the wheels is off, it causes the vehicle to veer to one side due to unequal tire wear or improper angles of the wheels. Additionally, drivers may notice that the steering wheel does not sit straight when driving on a level road, which is another sign that alignment issues are present.

Other signs, like a smooth ride quality, even tire wear, and increased fuel efficiency, do not indicate alignment problems. In fact, a smooth ride and even tire wear are signs that wheels are properly aligned, as they ensure balanced driving dynamics and even distribution of weight across the tires. Increased fuel efficiency similarly suggests that the vehicle is functioning optimally, which typically correlates with proper alignment. Hence, the presence of any steering issues points directly to the need for immediate attention to the vehicle's alignment.