ConsumErs usuAlly Don't know ____________.
A．whErE to Buy ChEApEr things
B．whAt mAtEriAls ArE nEEDED to improvE FinishED proDuCts
C．why thEy purChAsE somE ExpEnsivE proDuCts
D．thE BrAnD nAmEs oF proDuCts thEy Buy rEgulArly