Final answer:
A good that is always used with another good is known as a complement. Complements are used together and have a negative cross-price elasticity, meaning if the price of one increases, the demand for its complement decreases, illustrating a direct relationship between the two.d) Complement
Step-by-step explanation:
A good that is always used with another good is known as a complement. Complements are goods that are often used together because the consumption of one good tends to enhance the consumption of the other. Examples of complementary goods include breakfast cereal and milk, notebooks and pens, and gasoline and sport utility vehicles. An important aspect of complement goods is their negative cross-price elasticity: if the price of one increases, the demand for its complement typically decreases.
For instance, if the price of golf clubs rises, the law of demand dictates that the quantity demanded of golf clubs falls, which in turn reduces the demand for a complement like golf balls. Similarly, when the price for skis goes up, fewer people are interested in ski resort trips because the overall cost of engaging in skiing is higher. Conversely, a decrease in the price of a complement good like coffee can increase the demand for its complement, such as sugar.