下列哪种物质能成为免疫原（） A.与蛋白质结合的DNP B.与红细胞结合的青霉素代谢

关于呼吸系统的解剖和功能，以下说法正确的是（）。

A.呼吸系统由鼻、咽喉、气道和肺脏、胸廓（不包括膈肌）组成

B.呼吸系统以环状软骨上缘为界分为上呼吸道和下呼吸道

C.右肺共有3叶10个肺段；而左肺共有2叶8个肺段

D.肺泡是肺的基本单位

E.上、下呼吸道分别仅有气体传导和气体交换的功能

定义了二维表数组A(2 to 5，5)则该数组的元素个数为( )。

A．18

B．27

C．24

D．30

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.

What is the main topic of the passage

A．The relationship between a plant’s roots and its shoots.

B．What can be learned by growing roots in isolation.

C．How plants can be grown without roots.

D．What elements are necessary for the growth of plants.

在数据库技术中，实体集之间的联系可以是一对一或一对多的，那么“学生”和“可选课程”的联系为（）。

很多学生在考试中失败并不是因为他们的能力不够，而是因为压力太大。请根据你的亲身经历，谈谈你对压力的看法以及你应对压力的措施，词数120左右。