Many homeowners regularly add commercial fertilizers to their lawns and gardens to maintain a healthy balance of nutrients in soil. The widely available commercial fertilizers contain only macronutrients -- namely, nitrogen, phosphorus, and potassium. To remain healthy in the long term, soil for lawns requires the presence of these macronutrients and also trace amounts of micronutrients such as zinc, iron, and copper, which are depleted when grass clippings are raked up rather than allowed to decay and return to the soil. Which one of the following can be properly inferred from the statements above? ['Widely available commercial fertilizers are not alone sufficient to maintain a healthy balance of nutrients in soil for lawns where grass clippings are not allowed to decay and return to the soil.', 'Homeowners who rake up their grass clippings are unable to maintain the long-term health of the soil in their lawns and gardens.', "There is no single fertilizer that provides both the macronutrients and micronutrients necessary for maintaining soil's long-term health.", 'For soil to remain healthy in the long term, it requires the regular addition of both commercial fertilizers and a source of micronutrients such as grass clippings that are allowed to decay and return to the soil.']