What is essential for the common functionality of a motorcycle?

A motorcycle's essential functionality primarily depends on crucial safety features, among which working brakes are paramount. Brakes are vital for controlling the speed of the motorcycle, allowing for timely stops and ensuring the rider can react appropriately to road conditions or traffic situations. Without functional brakes, the risk of accidents significantly increases, making them a fundamental component of motorcycle safety and performance.

While features like turn signals, windshields, and windshield wipers contribute to the overall functionality and safety of the motorcycle, they are not as critical as brakes. Turn signals assist with communication and visibility to other road users, while a windshield can improve aerodynamics and rider comfort. Windshield wipers are generally irrelevant, as motorcycles do not have windshields that require wipers like cars do. Therefore, among the options provided, working brakes are the most essential for a motorcycle to function safely and effectively on the road.