Which of the following best describes a locking device?

• A. Improves fuel efficiency
• B. Prevents inadvertent movement
• C. Records voyage data
• D. Detects fuel leaks

Answer: (B)

The main idea is preventing unintended operation. A locking device is used to secure a control or mechanism so it cannot move or be activated by accident—whether from vibration, bumps, or rough handling—until someone intentionally releases it. This is a safety feature for valves, levers, switches, or circuit breakers, like a padlock on a valve handle or a lockout on a breaker. The other options describe outcomes that aren’t about preventing movement: improving fuel efficiency, recording voyage data, or detecting fuel leaks. So the best description is that a locking device prevents inadvertent movement.