The social process of determining who does what work and for what reward is called

I believe the answer is: Division of Labor.
Division of labor is always necessary because one part of the economic operation wouldn't be able to done without the completion of other parts, no matter how small it is.
For example, a manager of a big restaurant wouldn't be able to fulfill their revenue goals if the cashiers do not keep the money properly.

True is the correct answer

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.