Which of the following would cause toe-out-on-turns to be out of specification?

Toe-out-on-turns is a critical alignment specification that refers to how the front wheels of a vehicle behave during a turn. Specifically, it describes how the front wheels should angle outward when the vehicle is steered.

A bent steering arm can impact the angle at which the wheels turn in relation to each other. When the steering arm is bent, it alters the steering geometry, leading to one wheel possibly turning more or less than the other. This asymmetrical turn can create a situation where the toe-out-on-turns specification is affected, causing the wheels to not align correctly during turns.

In contrast, while bent tie rods, lower control arms, and upper control arms can influence the overall alignment and handling of the vehicle, they do not directly affect the specific relationship required for toe-out-on-turns in the same way that a bent steering arm does. Instead, these components generally affect the position of the wheels and how they sit relative to the vehicle's centerline, rather than specifically influencing the turn angles.

Thus, the bending of a steering arm is the most likely culprit in leading to a misalignment of toe-out-on-turns, making it the correct choice in this scenario.