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问题 单项选择题

根据《行政复议法》的规定，公民、法人或者其他组织认为具体行政行为侵犯其合法权益的，可以自知道该具体行政行为之日起( )日内提出行政复议申请；但是法律规定的申请其他期限超过( )日的除外。

A．30 30
B．30 60
C．60 60
D．45 60

答案

参考答案：C

解析： 公民、法人或者其他组织认为具体行政行为侵犯其合法权益的，可以自知道该具体行政行为之日起60日内提出行政复议申请；但是法律规定的申请其他期限超过60日的除外。

计算题

一匀磁场，磁场方向垂直于xy平面，在xy平面上，磁场分布在以O为中心的一个圆形区域内。一个质量为m、电荷量为q的带电粒子，由原点O开始运动，初速为v，方向沿x正方向。后来，粒子经过y轴上的P点，此时速度方向与y轴的夹角为30°，P到O的距离为L，如图所示。不计重力的影响。求磁场的磁感强度B的大小和xy平面上磁场区域的半径R。

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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.

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.
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