{$mEDiAurl} whAt is thE DisCussion mAinly ABout
A、gEnErAl FEAturEs usED to DEFinE whAt DEsErts ArE.
B、ChArACtEristiCs shArED By All typEs oF DEsErts.
C、thE EFFECts oF DEsErts on thE gloBAl ClimAtE.
D、DiFFErEnt FACtors thAt lEAD to thE FormAtion oF A DEsErt.