If an observer is on board while towing a skier, how many people must the vessel be rated to carry at minimum?

The correct choice indicates that if a vessel is towing a skier with an observer on board, it must be rated to carry a minimum of three people. This is based on safety regulations that ensure there is a designated operator, an observer, and the skier themselves. The operator is responsible for navigating the boat, while the observer plays a critical role in keeping an eye on the skier and ensuring their safety. This arrangement allows the observer to communicate any potential hazards or needs back to the boat operator.

The number of people the vessel can safely carry needs to accommodate these roles, along with the skier who is being towed. Therefore, a vessel rated for fewer than three individuals would not meet safety and legal requirements, as it wouldn't be possible to have both an operator and an observer present while towing a skier. This regulation helps prevent accidents by ensuring there is someone dedicated to watching the skier at all times.