About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the usual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course. The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deal of oxygen.The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In addition, roots can provide the shoots with organic nitrogen compounds. This comes in handy for the growth of buds in the early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can "export" protein to the rest of the plant in the form of amino acids.

The scientists found what the isolated roots need is________.

A．quite natural

B．sugar, minerals and vitamins

C．some rare vitamins

D．organic nitrogen compounds

田纳西河流域的气候条件对农业发展的影响，正确的是[ ]

A、夏季降水丰富，雨热同期，有利于农业生产

B、冬夏温差小，不利于农作物成熟

C、终年高温多雨，发展农业生产条件优越

D、夏季农作物生长旺盛，但降水相对较少