下列关于热量、内能与热值的说法中，正确的是 ( )
A．热量总是从内能大的物体向内能小的物体传递
B．在热传递过程中，物体向外传递100J的热量，其内能也将减小100J
C．热传递是改变物体内能的唯一途径
D．热值大的物体在完全燃烧的情况下放出的热量多
答案：B
题目分析：发生热传递的条件是存在温度差，热量总是从高温物体传到低温物体，A错；在热传递过程中，热量是转移的那部分内能，所以物体放出多少热量，内能就减少多少，B对；改变内能的方式有两种：做功和热传递，C错；燃料完全燃烧所放出的热量为
，所以热量不仅与热值有关，还和燃料的质量有关，D错。
| 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 underlined word "themselves" in Paragraph 1 refers to ______.
A．plant physiologists
B．solutions
C．laboratory flasks
D．roots