Aprimary source of getting specific information on a particular bill is

a. congressional records
b. constitution
c. your state representative
d. washington daily newspaper

A primary source is a source that is directly reporting a given event; not copied of paraphrased by someone else.

The primary source for the information on a specific bill is the A. Congressional Records - especially the information about how and why the bill was passed can be found there.  

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.