Final answer:
Adam Smith is the economist who argued that the economy should be left to manage itself in order to close a recessionary gap, which reflects his belief in the power of the free market driven by individual self-interest. The correct option is C.
Step-by-step explanation:
The economist who argued that the economy should be left to itself to close a recessionary gap is Adam Smith. He believed in the concept of the invisible hand, where unregulated markets are guided by individual self-interest and competition in a way that ends up benefiting society as a whole.
In contrast, John Maynard Keynes advocated for government intervention during economic downturns to stimulate demand and close the gap. Milton Friedman also supported free-market capitalism but focused more on the role of monetary policy and believed it should be allowed to grow in tandem with the economy.
Lastly, Karl Marx had an entirely different viewpoint, advocating for a classless society and the abolishment of capitalism.
Hence, Option C is correct.