What must be available for safe operation of any motorboat?

The correct choice is that a fully charged fire extinguisher must be available for the safe operation of any motorboat. This is essential because motorboats are equipped with engines and systems that can become flammable in the event of a fire, whether due to fuel leaks, electrical malfunctions, or an accident. Having a properly charged fire extinguisher allows for immediate action to extinguish small fires, which can prevent them from escalating and causing more significant damage or endangering the lives of passengers.

While other safety equipment, such as life jackets, is critical for personal safety on the water, the specific requirement for the operation of a motorboat emphasizes the importance of fire safety equipment. It is also important to note that while a first aid kit and a spare fuel can are useful for emergency situations or convenience, the critical focus for preventing and managing fire hazards directly falls on having a fully functional fire extinguisher onboard.