In the wealth of nations, smith writes about an “invisible hand.” which of the following best describes the “invisible hand”? a. a guide that ensures that people produce the things that society needs b. the way in which government duties secretly increase the price of imported goods c. the process by which a single worker completes all stages in the manufacture of a product d. the thefts committed by workers in factories.

The answer is A: a guide that ensures that people produce the things that society needs.

The theory behind Smith´s “invisible hand” is that offer and demand (what is produced and what is needed, in rough terms) are correlated in as much as self-interest (what one can produce for one´s own benefits) is channeled towards the needs that a given social group may experience at a given moment. This is indeed the justification for any form of laissez-faire economic system which dictates that commerce (transactions between private parties) should not be interrupted by governmental intervention since offer and demand balance each other "naturally".  

the anwser is a) to prevent military conflict