If the engine of a motorcycle seizes while in use, what should the motorcyclist do?

Answer: B — Apply the clutch to disengage the engine from the rear wheel.

When a motorcycle engine seizes, it can create a dangerous situation as the rear wheel may stop turning while the motorcycle is still in motion. By applying the clutch, the rider effectively disconnects the engine from the rear wheel, which allows them to maintain control over the motorcycle rather than experiencing a sudden loss of power that could lead to skidding or loss of control. This action facilitates a more manageable response to the situation. The motorcyclist can then choose to decelerate safely and gradually by using the brakes without risking a sudden jerk from the engine seizing. It creates a buffer that helps the rider to handle the motorcycle more safely until they can bring it to a stop. Other options, such as turning on the four-way flashers, would not provide immediate control over the motorcycle, and downshifting could exacerbate the problem by forcing the bike to potentially skid. Applying the brakes hard may lead to a loss of traction if the rear wheel is locked. Hence, disengaging the engine with the clutch is the most effective and safest response in this scenario.