A boathouse's grade-level portions require ____________ protection.

The correct answer is that a boathouse's grade-level portions require ground-fault circuit interrupter (GFCI) protection. This is important because GFCI devices are designed to protect individuals from electric shock in areas where water is present, such as in a boathouse. Since water and electricity pose a significant risk, GFCIs automatically shut off electrical circuits if they detect an imbalance in electrical current, which can occur if electricity is leaking to the ground, often through water.

In locations like boathouses, where moisture is a common factor, using GFCIs ensures safety for anyone who may come into contact with electrical devices or outlets while near or in water. This requirement is part of adhering to safety codes and best practices to mitigate the risks associated with potential electrical hazards in wet environments.