The possibility of living on Mars is being explored after a study proved the discovery of saltwater lakes below the surface of Mars.

Billions of years ago, the climate of Mars was warm and wet and had the possibility for hosting microbial (微生物的) life. Scientists are not 100 percent sure what happened to water on it. One popular general idea is solar (太阳的) wind. According to the idea, the solar wind likely blew away CO₂ as well as small drops of water from air on Mars over the past billion years, leaving the planet with only 10 percent of its beginning amount of water today.

It is just like when we get our skin wet and there are small drops of water on the surface, the wind will finally dry us off, and the water will be carried away. This is very likely to happen to Mars, causing the surface to become hard and dry.

This discovery was made with the help of the European Space Agency’s Mars Express spaceship, which sent out radio waves to the planet’s surface. Scientists decided what material their radio waves met with. The area with the supposed bodies of water had high reflectivity (反射率), which is why scientists believe that water is stored below the surface.

With temperatures as low as the average on Mars, water is supposed to be frozen. But scientists think that water on Mars is able to keep a water form because of the high level of the salt—so high that the possibility of active life surviving in such a condition is pretty low.

With the salty water and an unsuitable climate, Mars is now not fit to live on. But scientists are still trying to learn more about the life forms that once possibly lived on the planet.

1.41. What does the underlined word “it” refer to (指代) in paragraph 2?

A Earth.

B Solar surface.

C Mars.

D Microbial life.

解析：选C。本题为代词指代题。第二段前文一直在讲述火星远古有水，本句 “Scientists are not 100 percent sure what happened to water on it.”，it 指代前文的 Mars 火星，科学家不确定火星上面的水发生了什么，其余选项地球、太阳表面、微生物生命均不符合上下文逻辑。

2.42. Why is the human’s skin mentioned in paragraph 3?

A To explain the great influence of solar wind.

B To provide further information about Mars.

C To stress the importance of water on Mars.

D To suggest keeping skin from getting dry.

解析：选A。本题为写作手法题。第三段拿人的皮肤沾水后被风吹干来打比方，用来通俗解释太阳风是如何带走火星水分，体现太阳风带来的巨大影响。这个例子不是补充火星其他信息，不是强调水的重要性，也不是讨论保护皮肤，B、C、D 不符合段落目的。

3.43. How did the researchers prove there is water on Mars?

A By sending out the spaceship to Mars.

B By measuring the amount of salt on Mars.

C By checking the materials collected from Mars.

D By noticing the number of reflected radio waves.

解析：选D。本题为细节理解题。原文说明火星快车发射无线电波，通过分析无线电波接触的物质，发现疑似水域区域无线电波反射率高，以此推断地下有水。A 只是发射探测器，不是证明水存在的手段；文中没有测量盐分、收集火星实物样本，B、C 错误。

4.44. What do scientists think of the future living on Mars?

A Comfortable.

B Hopeful.

C Disappointed.

D Uncaring.

解析：选B。本题为推理判断题。文章表明火星现在不适合居住，但科学家依旧继续研究火星曾经可能存在的生命，可以看出人类对火星居住这件事仍抱有希望。comfortable 舒适的、disappointed 失望的、uncaring 漠不关心的都不符合作者态度。

5.45. What’s the best title of the passage?

A The Exploration of Energy on Mars

B The Situation of Living Things on Mars

C The Explanation of The Climate on Mars

D The Discovery of Saltwater Lakes on Mars

解析：选D。本题为主旨大意题。全文围绕火星地下咸水湖的发现展开，介绍火星水的变迁、探测手段、液态水的条件和居住现状。A 火星能源探索，B 火星生物生存状况，C 火星气候解析，均只是局部片段，不能概括整篇文章。