What is one crucial fluid that must be checked during the pre-trip inspection for safety?

During a pre-trip inspection, checking brake fluid is critically important for safety because the braking system is essential for controlling the vehicle effectively. The brake fluid must be at the correct level and in good condition to ensure that the brakes function properly; any low levels or contamination can lead to brake failure. In situations where quick stops or sudden braking is needed, having adequate and functioning brakes is vital to avoid accidents and ensure the safety of passengers and other road users.

Windshield washer fluid, while important for visibility, does not directly impact the vehicle’s ability to stop. Clutch fluid also plays a role in some vehicles but is less critical compared to brake fluid when it comes to overall safety. Engine oil is essential for the vehicle's performance and longevity but does not affect the immediate stopping power or control while driving. Thus, the focus on brake fluid checks during pre-trip inspections is primarily about ensuring the vehicle remains safe to operate on the road.