Which of the following is a required feature for a motorcycle?

A motorcycle is required to have at least one brake as a fundamental safety feature. The braking system is critical for the rider's ability to control speed and stop the motorcycle effectively, which is essential to ensure the safety of both the rider and other road users. Proper braking capability allows for quick reactions to unforeseen circumstances, such as traffic stops or obstacle avoidance. This requirement is part of maintaining safe operating standards for motorcycles.

While features such as a horn, tires, and a windscreen can enhance safety and comfort, they aren't universally mandated across all motorcycles. For instance, while a horn is useful for alerting others, it does not directly affect the motorcycle's operation. Similarly, high-performance tires and windscreens can benefit handling and rider comfort but are not stipulated as necessary features by law. Hence, the requirement of having brakes is paramount for the basic functionality and safety of the motorcycle.