If Erin's Income Decreases And,as a Result,she Chooses to Buy

If Erin's income decreases and,as a result,she chooses to buy fewer milkshakes per month at each price,then her demand curve will

A) shift to the right.
B) shift to the left.
C) not shift; instead, Erin will move along her demand curve downward and to the right.
D) not shift; instead, Erin will move along her demand curve upward and to the left.