ACCorDing to thE pAssAgE, whiCh oF thE Following BEhAviors is FrEquEntly ChArACtEristiC oF FunnEl ClouDs
A、DEsCEnDing From DiFFErEnt ClouD BAsEs.
B．oCCurring in isolAtED ArEAs.
C．lAsting A long timE.
D．oCCurring in groups.