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

A、Ifthehighpressuregaugereadingdecreases,itindicatesaleakinthehighpressuresectionoftheunloaderorinthecylindervalveseat.;
B、Ifthelowpressuregaugereadingdecreases,itindicatesaleakinthelowpressuresectionoftheunloaderorinthepipingequipment.;
C、Ifthereadingofthehighpressuregaugedecreasesandthereadingofthelowpressuregaugerises,itmeansthattheregulatingscrewisleaking.;
D、Applytheleakdetectionsolutiontothejoint.Ifbubblescontinuetoproduce,itindicatesthatairisleakinghere.