He most common economic system in the world is a

closed economy.
command economy.
market economy.
traditional economy.

The answer is: market economy.

Market economy refers to an economic system in which production, distribution, and investment is dictated by the forces of supply and demand (in which the two are correlated, so that, in an ideal sense, the greater the demand, the less the supply, and vice versa, but always aiming at balance). In principle, a market economy would allow for productive forces (more or less regulated by government), through competition, to balance themselves so that capital can be distributed amongst these forces.  

sir thomas more, venerated in the catholic church as saint thomas more, was an english lawyer, social philosopher, author, statesman, and noted renaissance humanist. he was also a councillor to henry viii, and lord high chancellor of england from october 1529 to 16 may 1532.

i would think the answer is between b and d i would say d sorry if wrong