What observations were made famous by Adam Smith in his book "The Wealth of Nations"?

Letter D is the correct answer to this number. Adam Smith, a famous economist, quoted in his book that firms and households are guided by some invisible hand that leads them to market outcomes that are favorable for them. And that invisible hand is the prices to which a person makes a decision what he or she will buy or sell.

Because of these prices, people or the society actively participate on economic activities just by buying a carton of milk in the supermarket or selling their pre-loved car to a dealership thus making an impact on how strong their country’s economy is. It is how capable the people in strengthening their country’s economic power.