Which of the following is NOT a key component of a scuba diving system?

A snorkel is not a key component of a scuba diving system, as it is primarily used for surface swimming rather than for underwater diving. In scuba diving, the main focus is on equipment that supports the diver at depth where breathing underwater is necessary.

The regulator is essential for delivering air from the tank to the diver at the appropriate pressure for breathing. The tank stores the compressed air that the diver relies on for breathing during a dive. The buoyancy control device (BCD) is crucial for managing buoyancy and allows divers to ascend, descend, or maintain their depth effectively. While a snorkel can be a useful tool for surface swimming and conserving air before diving, it does not play a role in the actual scuba diving system needed for breathing underwater.