What event finally led the united states to enter world war two?

the answer is d. tariffs were raised by america's trading partners after the smoot-hawley tariff act, decreasing exports, and declining job rates.

crop rotation kepy different plants in the soil instead of once constintly. when switching out plants you have different nutrients being absorbed at different speeds and different roots growing differently therfore the spoil and water flow have to adapt and carry fresh nutrients to carry the constant changes that were going on in the soil.