The correct answers are Pairs of Substitutes: tea- coffee, butter-margarine, petroleum-natural gas; Pairs of Complementary goods: printer-ink cartridge, pen-refill
Explanation:
In economics and related fields, substitutes are goods or products that are considered similar by customers and due to this, one product can replace the other. For example, butter and margarine are substitutes because they have similar properties and uses, which makes one product replace the other. This also occurs with tea and coffee, and petroleum and natural gas because one product can replace the other. Also, because of this, it is common customers buy only one of the products rather than both depending on preferences, price, availability, etc.
On the other hand, complementary goods are those that are used together, this often implies customers buy the two products and changes in one product affect the other. This occurs in the case of printer and ink cartridge because the products are used together and buying a printer often implies customers need to buy the cartridges. Similarly, pens and refills for pens are used and bought together, and one cannot replace the other.
