Soil scientists studying the role of compost in horticulture have found that, while compost is useful for building soil structure, it does not supply large enough quantities of the nutrients essential for plant growth to make it a replacement for fertilizer. Many home gardeners, however, have found they can grow healthy and highly productive plants in soil that lacked essential nutrients by enriching the soil with nothing but compost. Which one of the following, if true, most helps to explain the discrepant findings of the soil scientists and the home gardeners? ["Most plants grown in home gardens and in scientists' test plots need a favorable soil structure, as well as essential nutrients, in order to thrive.", 'The findings of soil scientists who are employed by fertilizer manufacturers do not differ widely from those of scientists employed by the government or by universities.', 'Some of the varieties of plants grown by home gardeners require greater quantities of nutrients in order to be healthy than do the varieties of plants generally grown by the soil scientists in test plots.', 'Compost used in research projects is usually made from leaves and grass clippings only, whereas compost used in home gardens is generally made from a wide variety of ingredients.']