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OFFICIAL51 Look at the four squares [[■]] that indicate where the following sentence could be added to the passage. Where would the sentence best fit? Click on a square [[■]] to add the sentence to the passage.

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Surface Fluids on Venus and Earth
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A fluid is a substance, such as a liquid or gas, in which the component particles (usually molecules) can move past one another. Fluids flow easily and conform to the shape of their containers. The geologic processes related to the movement of fluids on a planet's surface can completely resurface a planet many times. These processes derive their energy from the Sun and the gravitational forces of the planet itself. As these fluids interact with surface materials, they move particles about or react chemically with them to modify or produce materials. On a solid planet with a hydrosphere and an atmosphere, only a tiny fraction of the planetary mass flows as surface fluids. Yet the movements of these fluids can drastically alter a planet. Consider Venus and Earth, both terrestrial planets with atmospheres.

Venus and Earth are commonly regarded as twin planets but not identical twins. They are about the same size, are composed of roughly the same mix of materials, and may have been comparably endowed at their beginning with carbon dioxide and water. However, the twins evolved differently largely because of differences in their distance from the Sun. With a significant amount of internal heat, Venus may continue to be geologically active with volcanoes, rifting, and folding. [■] However, it lacks any sign of a hydrologic system (water circulation and distribution): there are no streams, lakes oceans or glaciers. [■] Space probes suggest that Venus may have started with as much water as Earth, but it was unable to keep its water in liquid form. [■] Because Venus receives more heat from the Sun, water released from the interior evaporated and rose to the upper atmosphere where the Sun's ultraviolet rays broke the molecules apart. [■] Much of the freed hydrogen escaped into space, and Venus lost its water. Without water, Venus became less and less like Earth and kept an atmosphere filled with carbon dioxide. The carbon dioxide acts as a blanket, creating an intense greenhouse effect and driving surface temperatures high enough to melt lead and to prohibit the formation of carbonate minerals. Volcanoes continually vented more carbon dioxide into the atmosphere. On Earth, liquid water removes carbon dioxide from the atmosphere and combines it with calcium, from rock weathering, to form carbonate sedimentary rocks. Without liquid water to remove carbon from the atmosphere, the level of carbon dioxide in the atmosphere of Venus remains high.

Like Venus, Earth is large enough to be geologically active and for its gravitational field to hold an atmosphere. Unlike Venus, it is just the right distance from the Sun so that temperature ranges allow water to exist as a liquid, a solid, and a gas. Water is thus extremely mobile and moves rapidly over the planet in a continuous hydrologic cycle. Heated by the Sun, the water moves in great cycles from the oceans to the atmosphere, over the landscape in river systems, and ultimately back to the oceans. As a result, Earth's surface has been continually changed and eroded into delicate systems of river valleys - a remarkable contrast to the surfaces of other planetary bodies where impact craters dominate. Few areas on Earth have been untouched by flowing water. As a result, river valleys are the dominant feature of its landscape. Similarly, wind action has scoured fine particles away from large areas, depositing them elsewhere as vast sand seas dominated by dunes or in sheets of loess (fine-grained soil deposits). These fluid movements are caused by gravity flow systems energized by heat from the Sun. Other geologic changes occur when the gases in the atmosphere or water react with rocks at the surface to form new chemical compounds with different properties. An important example of this process was the removal of most of Earths carbon dioxide from its atmosphere to form carbonate rocks. However, if Earth were a little closer to the Sun, its oceans would evaporate; if it were farther from the Sun, the oceans would freeze solid. Because liquid water was present, self-replicating molecules of carbon, hydrogen, and oxygen developed life early in Earth's history and have radically modified its surface, blanketing huge parts of the continents with greenery. Life thrives on this planet, and it helped create the planet's oxygen- and nitrogen-rich atmosphere and moderate temperatures.

13.Look at the four squares [[■]] to add the sentence to the passage.

Venus may not have always been this way..

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正确答案:B
题目解析:
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【题目翻译】看四个正方形[■]把句子加到短文中。 A:金星可能也并不总是这样。 【判定题型】:根据题目问法,题目要求将句子插入到文中最恰当的空格处,故判断本题为句子插入题。 【待插入句分析】待插入句的意思是“金星可能也并不总是这样。” 【原文分析】意思是:由于大量的内热,金星可能继续与火山,裂谷和褶皱地质活动。但是,它没有任何水文系统(水的循环和分布)的迹象:没有河流、湖泊、海洋或冰川。空间探测器表明金星的起始水量可能和地球一样多,但是它无法保持水的液态。因为金星从太阳接收到更多的热量,从内部释放的水蒸发并上升到上层大气,在那里太阳的紫外线将分子分裂开。所以B方框后一句话说航天探测器显示,金星和地球的含水量在开始的时候可能是一样的。这两句话存在转折关系。 【选项分析】 A方框前面一句话是在说金星的地质活动活跃,A方框后一句话转折说金星上没有水文系统。从句意方面看,句子插在A处显然不合适。 B方框前一句话说金星上没有水文系统。而B后一句话说航天探测器显示,金星和地球的含水量在开始的时候可能是一样的。这两句话存在转折关系。故句子插在B处最合适。——“金星可能并不一直是这样(没有水文系统)的,一开始金星和地球一样也含有水。” C方框和D方框前后的内容都是在讨论为什么金星上没有水。逻辑非常完整,不需要再插入句子了,所以C、D排除。

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