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问题 单项选择题

直线

与平面π：x+y+2z-7=0的夹角为______

A．π
B．


C．


D．

答案

参考答案：D

解析：[考点] 空间直线与平面的夹角
l的方向向量为

，π的法向量为

，设直线l与平面π的夹角为φ，则

.
故

，选D.

多项选择题

下列选项中，属于委托代理终止的情形有()。

A.代理期间届满或者代理事务完成

B.被代理人死亡

C.代理人死亡

D.代理人丧失民事行为能力

E.被代理人取消委托或者代理人辞去委托
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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 free 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 withorganic 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.

Roots have the ability to ______.

A．make proteins

B．obtain fresh air

C．produce inorganic nitrogen

D．carry out activities without energy
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