The correct answer is B) pools and rebates.
Pools and rebates kept shipping prices high and frustrated farmers.
In railroad terms, pools were agreements between railroad owners to split the business and maintain elevated prices to have better income. One of the better-known cases in the 1800s was the Chicago-Omaha pool, to dissuade other competitors in 1870. Rebates also affected small companies because they could not afford to offer rebates and bigger companies could, so the business was for those big companies. Farmers were no rich people, to the opposite, they lived in a modest way and were very angry with the elevated prices railroads charged them to transport their goods.
The other options of the question were A) pools and imported goods. C) pools and tariffs. D) none of the above.