Answer:
a. self interest
Step-by-step explanation:
Adam Smith was a Scottish political economist, social and moral philosopher, author and he is famously considered to be the father of modern economics. Smith was born on the 5th of June, 1723 in Kirkcaldy, United Kingdom and he died on the 17th of July, 1790 in Panmure House, Edinburgh, United Kingdom.
In his first book titled, "The Theory of Moral Sentiments" which was published in 1776, he proposed the idea of an invisible hand, based on the tendency of free market economy to regulate or self-adjust themselves through demand and supply, competition, and self interest.
Hence, Adam Smith believed that self interest would lead to the production of items that consumers want.