Before mounting the motorcycle, which of the following checks is crucial?

Checking fluids and lights before mounting the motorcycle is crucial as it ensures the motorcycle is in proper working condition. By verifying fluid levels, such as oil and brake fluid, you can prevent mechanical failures that could lead to unsafe riding situations. Additionally, checking the lights ensures that both the front and rear signals are functioning properly, which is vital for visibility and signaling intentions to other road users. This pre-ride inspection helps identify any potential issues that could threaten your safety or the safety of others while riding.

While adjusting the seat, checking tire pressure, and inspecting the helmet are also important aspects of motorcycle preparation, they do not encompass the overall safety checks that directly affect the motorcycle's operability like checking fluids and lights does. Ensuring your fluids are at proper levels and your lights are functional is a fundamental practice for safe riding.