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问题 单项选择题

如果要在太阳系的行星中建一个人类居住点，下列行星中条件较适宜的是（）

A.天王星

B.木星

C.土星

D.火星

答案

参考答案：D

解析：

行星中与地球在质量、体积、密度等方面最为接近的是火星，故D正确。

考点：地球的特殊性。

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.

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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单项选择题

一定地质时期，一定的沉积环境中，一系列成因相近的相（亚相或微相）在剖面上组合关系称为（）。

A.相标法

B.相模式

C.相层序
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