Answer:
d. Complements
Step-by-step explanation:
Compliments or complementary goods are products that are used together. The use of one product is dependent on the availability of the other. Examples of complementary goods are cars and petrol, printers and ink cartridges, and computer hardware and software.
Changes in the price of a complementary product will affect the demand for the other product. If the price of cars decreases, leading to an increase in demand, the demand for petrol will automatically increase. The demand for complimentary products is described as joint demand.