Question

products and services that are used together. when the price of one falls, the demand for the other increases (and conversely). choose an answer public goods unrelated goods complementary goods substitute goods

Explanation:

The question describes goods that are used together, and when the price of one falls, the demand for the other increases. This matches the definition of complementary goods. Public goods are non - excludable and non - rivalrous, unrelated goods have no demand relationship, and substitute goods are used in place of each other (where a price drop in one would decrease demand for the other).

Answer:

complementary goods