The grocery store wants to increase the demand for ice cream cones, so it puts ice cream on sale. this shows that the grocery store owner thinks that ice cream and ice cream cones are

a complements
b substitutes
c unrelated

a. complements

Complementary goods are those that consumers believe to go well together. As these items are often bought together, when the price of one goes down, the demand for the other one usually increases, depending on how intertwined they are. In this case, ice cream and ice cream cones are usually sold together, so they are considered complements.

not to sure thinking it would be a hope this