Answer:
b. A rise in the price of popsicles, a substitute for ice cream.
Step-by-step explanation:
A shift in the demand curve to the right indicates an increase in demand.
If the price of a subsituite increases, demand increases.
An unexpected cold reduces demand and shifts the demand curve to the left.
Changes in price leads to movement along the demand curve.
A reduction in cost of production affects the supply curve.