某生产经营单位的市场部门正在开展合格供应商的选择评价，按照《职业健康安全管理体系》(OHSAS18001)的运行模式，该项工作属于体系运行的( )阶段。

A．策划

B．实施与运行

C．检查与纠正措施

D．管理评审

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.

Which of the following best describes the organization of the passage

A．The results of two experiments are compared.

B．A generalization is made, and several examples of it are given.

C．The findings of an experiment are explained.

D．A hypothesis is presented, and several means of proving it are suggested.