Final answer:
While riding, passengers should actively participate in maintaining balance and stability, similar to the rider. They should lean with the rider, effectively increasing the change in momentum and keeping the overall system weight balanced. A firm hold and controlled movement are also necessary.
Step-by-step explanation:
The best advice for a passenger while riding is c) Passengers should hold onto the rider's shoulders and lean with them. This is because the passenger, just like the rider, should participate in providing the stability needed for a smooth ride. As explained in the turning of a bicycle, the rider and the bicycle lean at a particular angle to keep a line from the center of gravity going through the ground's exerted force. With the passenger also leaning, the system's weight remains balanced and the perpendicular components of the force on the bicycle wheel maintain stability.
When the passenger leans with the rider, they not only reduce the risk of injury to themselves by increasing the change in momentum, but also aid in creating an overall balanced system. The passenger and the rider should indeed move as one unit.
While it's also important for passengers to comply with safety procedures of maintaining a firm hold on the rider and not to move excessively or unpredictably, their active participation in the ride maintains balance and stability, which is the key to a safe ride.
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