Which leak detection operations of high pressure gas cylinder are correct?

A、If the high pressure gauge reading decreases, it indicates a leak in the high pressure section of the unloader or in the cylinder valve seat.;

B、If the low pressure gauge reading decreases, it indicates a leak in the low pressure section of the unloader or in the piping equipment.;

C、If the reading of the high pressure gauge decreases and the reading of the low pressure gauge rises, it means that the regulating screw is leaking.;

D、Apply the leak detection solution to the joint. If bubbles continue to produce, it indicates that air is leaking here.