Final answer:
When two resources are highly suitable for one another as complements, a decrease in the price of one increases the demand for the other. This occurs because consumers tend to purchase more of both goods when they are used together, like bread and peanut butter.
Step-by-step explanation:
If two resources are highly suitable for one another and are considered complements, the correct answer to how their demand and cost of production will be affected by a change in price is found by understanding the relationship between the price of goods and their demand. When the price of a complementary good decreases, consumers tend to buy more of both goods because they are used together. Therefore, a decline in the price of one will increase the demand for the other. Conversely, an increase in the price of one will typically reduce the demand for its complement. Using the example of bread and peanut butter, a decrease in the price of peanut butter will lead to an increased demand for bread, because these two products are often consumed together. This illustrates how complementary goods impact each other's markets.