Choice "c" is correct. A rise in the price of a complementary commodity would cause a shift to the

left in any demand curve (representing decrease in demand, at all price levels, for that product).

With respect to complementary goods, the demand for the primary product is directly impacted by

the demand (and hence the price changes) for the complementary goods. For instance, if the price of

gasoline goes up, the demand for cars will decrease, causing the demand curve for cars to shift left.

Choice "a" is incorrect. A rise in the price of a substitute product will make the demand curve shift to

the right.

Choice "b" is incorrect. A rise in average household income would make the demand curve shift to

the right, representing an increase in demand.

Choice "d" is incorrect. A rise in population, or a change in consumers' tastes in favor of the

commodity are also changes that may cause an increase in demand, making the demand curve shift

to the right.