单选题 {{B}}Text 5{{/B}}

The air surrounding us is important to everyone. Without air, we could not exist. Everyone understands that. But air is necessary in many other ways — ways that are not always so obvious or widely known.
If we did not have air, there would be no sound. Sound travels through air. Where there is no air, there is no sound. Without air there would be no fire. There would be no automobiles, since motors need air in order to operate.
Without air, there would be no wind or clouds. The night time would be very cold and the days very hot. We would be forced to seek shelter from the sun, as there would be no atmosphere to protect us from the sun's deadly rays.
In this huge ocean of air surrounding the earth, there is more energy than in all the coal, oil and gas we have on the earth. Electrical energy is collected in the atmosphere as water is collected and stored in a dam (大坝). The existence of electricity in the air has been known for centuries. Men have gazed in wonder at the bright patterns of lightening in storm clouds. But thorough (彻底的，深入的) study of electricity in the air was not possible until the development of radio.

单选题 It is not widely known that ______.

【正确答案】 C

【答案解析】[解析] 本题考查对句意的理解。根据文章第一段最后一句“But air is necessary in many other ways—ways that are not always so obvious or widely known”，可以得出答案[C]与其句意相符合。

单选题 Without air protection, the sun's rays ______.

【正确答案】 D

【答案解析】[解析] 本题考查文中的细节。根据文章第三段最后一句“‘We would be forced to seek shelter from the sun，as there would be no atmosphere to protect us from the sun's deadly rays”．可以判断答案为[D]。其中理解deadly 也是个关键，它的意思是“致命的”，可以得知Without air protection， the sun's rays will do harm to human beings(如果没有空气的保护，太阳光线会伤害我们)。

单选题 The existence of electricity in the air has been known ______.

【正确答案】 A

【答案解析】[解析] 本题考查对句意的理解。文章第四段第三句“The existence of electricity，in the air has been known for centuries”就是答案所在的地方。其中，理解for centuries是个关键，其意思是“好几个世纪，好几百年”，所以答案为[A]。

单选题 According to the passage, which of the following is NOT true?

【正确答案】 C

【答案解析】[解析] 是非判断题。本文主要解释了空气对于地球上生命的重要性。[A]、[B] 两项可以从文章的第一、二段找到依据，而[C]、[D]项则在最后一段。其中[C]项与内容“But thorough(彻底的，深入的)study of electricity in the air was not possible until the development of radio”不符。所以答案是[C]。