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问题 问答题

简述课堂教学中提高知识直观的方法。

答案

参考答案：灵活运用多种直观形式;加强词与形象的配合;运用感知规律，突出直观性对象的特点;培养学生的观察能力;让学生充分参与直观过程。

选择题

地球自转和昼夜更替的周期分别是

A．1 恒星日和1 太阳日

B．1恒星日和12时

C．1太阳日和1恒星日

D．12时和1太阳日
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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.

Approximately how much of the Earth’s atmosphere is nitrogen

A．One-fourth.

B．One-half.

C．Three-fourths.

D．All of it.
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