The groups that have been affected mostly in railroads and monopolies are small farmers shipping crops to local markets
Option (a);
EXPLANATION:
Railroad pools refers to association of competing railroads, in which competitive business are divided by dividing traffic but by diving the income.Farmers were the ones who were most harmed with these railroads as earning had become extremely difficult for them.
They had no way to transport their crops, so they had to travel in trains and railroad companies would charge them higher than normal customers. To avoid the damage of crops, farmers used to pay such high prices. So, farmers wanted the government to regulate the prices of these railroads.