Which device assists divers in regulating airflow underwater?

The device that assists divers in regulating airflow underwater is the regulator. A regulator is a crucial piece of diving equipment that reduces the high-pressure air from the tank to a breathable pressure, allowing divers to inhale air comfortably and safely while submerged. It ensures that the diver receives air at a consistent and manageable pressure, which is vital for preventing complications such as lung overexpansion during ascent.

The mechanism of a regulator allows it to adjust the airflow based on the diver's needs, providing air when the diver inhales and reducing resistance when they exhale. This functionality is essential for maintaining proper breathing and supporting the diver’s overall safety and comfort underwater.

The other options, while important for different functions in diving, do not regulate airflow. A buoyancy compensator helps manage a diver's buoyancy, a dive computer provides vital information about depth and time, and a weight belt is used to help the diver achieve neutral buoyancy by offsetting the buoyancy of the wetsuit or drysuit. Each of these plays a significant role in scuba diving, but the regulator specifically addresses the regulation of airflow.