Explanation:

- Option 1: John Keynes

- John Maynard Keynes was a British economist. He is known for his work on modern macroeconomics and the philosophy of Keynesian economics.

- Option 2: Karl Marx

- Karl Marx was a philosopher and economist known for his theories about capitalism and communism, mainly through his works "The Communist Manifesto" and "Das Kapital."

- Option 3: Amartya Sen

- Amartya Sen is an Indian economist and philosopher, known for his contributions to welfare economics and social choice theory. He won the Nobel Prize in Economic Sciences.

- Option 4: Adam Smith

- Adam Smith is the correct answer. He was a Scottish economist and philosopher who wrote "An Inquiry into the Nature and Causes of the Wealth of Nations," a foundational text in classical economics.