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问题 单项选择题

工作面的大小表明（）。

A.空间位置的多少

B.能划分施工段的多少

C.能完成工程量的多少

D.能安排施工人数或机械台数的多少

答案

参考答案：D

解析：本题考查的是流水施工参数。工作面的大小，表明能安排施工人数或机械台数的多少。

单项选择题

在效用水平不变的条件下，消费者增加消费一个单位的某商品时，必须放弃的另一种商品的消费数量称为（）

A.边际效用

B.商品边际替代率

C.边际成本

D.边际技术替代率
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单项选择题

As viewed from space, the Earth’’s distinguishing characteristics are its blue waters and white clouds. Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life. Circling the Sun at an average distance of 149 million km (93 million miles), the Earth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid spin and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in the Earth’’s atmosphere before they can strike the surface. The planet’’s active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formed. The Earth has a single natural satellite — the Moon.

Which of the following helps to create the Earth’s magnetic fields

A．Its blue waters.

B．Its nitrogen atmosphere.

C．Its molten metal core.

D．The Moon.
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