d- inflation would not increase the farmers debt, but (unless the debt is adjusted for inflation) the debt would decrease - this is not a correct answer.
Inflation is the decrease of the value of money (but the value of objects and services stays the same - it increases with the respect to the value of the money. Because of this neither the manufactured goods nor the farm machinery would be cheaper- but the increase of crop prizes would take place (so answer a), and that's why farmers favour it.