Final answer:
When the price of ham falls, the demand for its complement, cheese, increases due to their combined consumption.
Step-by-step explanation:
When ham and cheese are complements, if the price of ham falls, the demand for cheese increases. This is because a lower price for ham encourages consumers to buy more ham, and since these goods are used together, their consumption tends to enhance each other. Therefore, as more ham is purchased due to its lower price, consumers are likely to purchase more cheese to complement their increased ham consumption.
The correct answer to the question is A. the demand for cheese increases.