The book 'An Enquiry into the Nature and Causes of the Wealth of Nations' is written by:

1. J. M. Keynes
2. David Ricardo
3. Adam Smith
4. Karl Marx

Option 1: J. M. Keynes -> Known for "The General Theory of Employment, Interest and Money" (1936), not this book.

Option 2: David Ricardo -> Wrote "On the Principles of Political Economy and Taxation" (1817), not this book.

Option 3: Adam Smith -> Author of "The Wealth of Nations" published in 1776.

Option 4: Karl Marx -> Famous for "Das Kapital", not this book.

Hence, Option 3: Adam Smith -> Adam Smith published "An Enquiry into the Nature and Causes of the Wealth of Nations" in 1776, which is considered the foundation of modern economics. This seminal work introduced concepts like the "invisible hand," division of labor, and free market economics, making Smith known as the father of modern economics.-> correct