The correct answer is C. 1776.
Adam Smith’s major work, An Inquiry into the Nature and Causes of the Wealth of Nations, was published in 1776. It is considered one of the most important books ever written on economics. In it, Smith argues that the wealth of a nation is not determined by the amount of gold and silver it possesses, but rather by the productivity of its people. He also argues that the free market is the best way to organize an economy, as it allows for the efficient allocation of resources and the division of labor.
The other options are incorrect. Option A, 1756, is the year that Smith’s Theory of Moral Sentiments was published. Option B, 1766, is the year that Smith was appointed as a commissioner of customs in Scotland. Option D, 1786, is the year that Smith died.