Explanation:

- Option 1: 1930

- In 1930, John Maynard Keynes published "A Treatise on Money," a significant work in economic literature, but not his most famous book.

- Option 2: 1931

- This year does not align with any major publication by Keynes. No notable book of his was released during this year.

- Option 3: 1936

- John Maynard Keynes published his most famous book, "The General Theory of Employment, Interest, and Money," in 1936. It revolutionized economics and laid the foundation for modern macroeconomics.

- Option 4: 1940

- Keynes released "How to Pay for the War" in 1940, which addressed the economic strategies for World War II.