ACCorDing to thE pAssAgE wE CAn sEE thAt lowEr priCEs AnD BEttEr quAlity oCCur _____.
A．As A rEsult oF thE EFFECt oF onE on thE othEr
B．AlwAys At thE sAmE timE
C．inDEpEnDEntly oF EACh othEr
D．whEn thE DEmAnD ExCEEDs thE supply