Which of the following politicians is most associated with fighting for causes that affected u. s. farmers?
a. william mckinley
b. theodore roosevelt
c. william boss tweed
d. william jennings bryan

The correct answer is letter D. William Jennings Bryan. He is the politician who is most associated with fighting for causes that affected U.S. farmers. He was an American orator and at the same time a politician. He is a dominant force in the populist wing of the Democratic Party.

The correct answer to your question is d - William Jennings Bryan. 

William Jennings Bryan was notorious as a politician for arguing and considering the "farmers' side of the story". He fought for causes which helped them in various ways.