Please choose the correct answer to the question: Planting legumes in order to add nitrogen to soil most likely causes

Answer1: a decrease in the amount of acid rain. Answer2: an enrichment in the fertility of the soil. Answer3: an increase in the ratio of nitrogen to oxygen in the system. Answer4: a reduction in the soil's ability to manufacture its own nitrogen.

Answer format: answer1/answer2/answer3/answer4
Answer: answer2