Which of the following is an example of an active restraint?

An active restraint is a safety feature designed to actively protect the occupants of a vehicle during a collision. A seatbelt exemplifies an active restraint because it requires the driver and passengers to engage it manually before driving. When properly fastened, a seatbelt helps secure the occupants in their seats, reducing the likelihood of injury during an accident by keeping them firmly in place and preventing them from being thrown around inside the vehicle or ejected from it.

In contrast, an airbag deploys automatically in the event of a crash, making it a passive restraint; while it enhances safety, it does not require any action from the occupant. Child safety locks, while vital for child safety, also operate without the need for active engagement from occupants. Anti-lock brakes serve a different purpose by preventing wheel lockup during hard braking, but they do not provide direct restraint to the occupant themselves in the event of a collision.

Therefore, a seatbelt stands out as the correct answer because it demands active participation from the vehicle's occupants and plays a vital role in their restraint during a crash.