Explanation:
Complements and Substitutes are basically the goods or services. Complements are the goods which are used with one another, and with the increase of price of one good, the demand of other good falls. On the other hand, substitutes are the goods which are used in place of other goods and with the increase in the price of one good, the demand of other product increases.
In this question, Mobile Applications and Smart Phones are Complements, and Smart Phones and Conventional Phones are Substitutes, and Mobile Applications and Conventional Phones are substitutes.
