GRE

The surface of Venus calcite, a mineral that absorbs the gas sulfur dioxide. Sulfur

dioxide is often produced by volcanic activity and is plentiful in Venus’atmosphere, so

there must be a source, perhaps volcanic, producing sulfurdioxide on Venus.

1. Whichof the following is an assumption on which the argument depends?

A. In the recent past, the level of sulfur dioxide in Venus’ atmosphere was notmuch

higher than it is now.

B. If there is volcanic activity on the surface of Venus, it is not adequate tomaintain the

observed amount of sulfur dioxide in the atmosphere.

C. The sulfur dioxide in Venus’ atmosphere forms clouds that prevent direct observation of the surface.

D.Sulfur dioxide produced by volcanic activity on the Earth’s surface is also absorbed by minerals other than calcite.

E.The calcite on the surface of Venus is in sufficient supply to continue to absorb sulfur

for millions of years to come.

该题是一道假设题。文章说，金星大气中有很多二氧化硫(sulfur dioxide ), 二氧化硫经常由火山活动产生，由C(calcite )吸收。文章由此得出结论：金星表面应该有来源，很可能是火山，正在产生二氧化硫。

文章推理依据什么假设呢?

解析

从文章内容可知，决定现在金星大气中是否有二氧化硫有两个关键因素：

1输入(例如火山喷发)，2 输出(被C吸收掉)。

文章关键推理是：从现在大气中有二氧化硫，直接推出现在有输入(关键因素1起作用)。问题很可能出在哪里?对啦，忽略了输出的问题(关键因素2)。

A选项说，最近的过去，金星大气中二氧化硫的水平不比现在高很多。这就是针对了输出的问题(关键因素2)。如果是(过去比现在水平高很多)，就是输出(被C吸收掉)在起作用。也就是说，未必现在是有输入的(关键因素1)。作者的结论就被严重削弱了。

所以，A是正确选项。看懂了么?再琢磨一下。

E选项说，金星表面的C有充足的供给，未来几百万年能继续吸收硫。

该选项无关。文章讨论的是二氧化硫的问题，不是“硫”。

退一步说，等同“硫”和二氧化硫。说C丰富，是直接削弱文章推理思路，不是文章推理所需要的假设：把可能削弱文章推理的可能性否定掉。

（责任编辑：）

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