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问题 选择题

—When does the law           ?    

—On the first day next year.     [ ]

A. come into being    

B. come into operation    

C. come into action    

D. come into sight

答案

答案：B

单项选择题

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 word "intact" in Paragraph 2 is closest in meaning to________.

A．mature

B．wild

C．whole

D．tiny
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单项选择题

一个物体沿直线运动，它的速度图象如图所示，由此可知（）

A.1s时物体返回出发点

B.2s时物体运动方向发生改变

C.前3s内物体的位移为0

D.前2s内和第4s内物体运动的加速度大小相等
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