What condition will result in rejecting a vehicle during inspection?

The correct answer highlights a condition that directly affects the safety and compliance aspects of a vehicle's lighting system. Auxiliary lights are intended to provide additional illumination beyond standard lighting; however, if they emit a beam that is excessively bright, it can create glare for other drivers, posing a safety hazard. This situation contravenes regulations pertaining to vehicle lighting standards, thus justifying a rejection during inspection.

In the context of vehicle safety and compliance, functioning brake lights and horns are indeed critical components, and a vehicle with less than three brake lights or a malfunctioning horn may also be subject to rejection. However, the specific concern around auxiliary lights' brightness is related to the broader principle of ensuring that all vehicular features promote safe operation and do not interfere with other road users. The reference to illegal tread depth on tires points to an equally important safety issue, yet the option regarding the brightness of auxiliary lights speaks to a particular rule regarding light emissions that can impact other drivers.