A soil can be low in ammonium and potassium ions because of increased acidity of the soil. The acidity is caused by hidrogen (H) and Al (alluminuim) ions. There few causes: acid rain, nitrate leaching, rainfall, decompositions of organic matter (leaves, corps etc) due to microorganism activity.
The completed sentence with the correct answer is; How does the first sentence in the paragraph help to introduce the main idea. The correct answer is B.
