题目内容：

NASA on September 28, 2015 announced the strongest evidence yet for liquid water on the red planet, increasing the possibility that astronauts journeying to Mars could someday rely on the planet's own water for their drinking needs.

    You may feel like you've heard about the hunt for liquid water on Mars before—and the researchers involved know it may seem played out. But science has yet to truly prove that water flows on Mars once and for all, and doing so could completely change the way we view the planet. This new data is a big step in the right direction.

"Liquid water is an attractive topic, and we like the thousandth time someone has discovered water on Mars," Lujendra Ojha, the Georgia Tech PhD candidate who led the research announced Monday, told The Post. But there's a good reason that liquid water is so "attractive": Mars is now the only planet in our solar system to show evidence of the stuff on its surface, other than our own. Other worlds have it in subsurface oceans, or scattered around as vapor in the atmosphere. But Mars is the only place where we have solid evidence for liquid that sits right there in the open air. While it would be a major leap to suggest that Mars might harbor life—even microbial life—liquid water at least makes it possible that parts of the planet are habitable.

     The study builds on research from April, when scientists using data from the Curiosity rover noted that the planet had the seasonal potential for liquid water. We know that because of the extremely low pressure on Mars, water has a boiling point of just a few degrees Celsius, after which it evaporates. The April study noted the presence of perchlorates (高氯酸盐) —a kind of salt—which could make the boiling point of Mars' water much higher, theoretically allowing it to remain liquid. They affirmed that the planet's temperature would be right for liquid, perchlorate-filled water to form every day during winter and spring.

1.What does the Paragraph 2 mainly tell us?

A. The significance of the discovery.

B. The doubt of the discovery. 

C. The difficulty of the discovery.

D. The expense of the discovery.

2.The underlined words "our own" in Paragraph 3 refer to ________.

A. Mars

B. the earth

C. liquid water

D. the solar system

3. What plays an important role in making Mars' water in the state of liquid?

A. The thick atmosphere around Mars.

B. The physical structure of Mars.

C. The extremely low pressure on Mars.

D. Perchlorates in Mar's water.

4. The best title for the passage can be "________".

A. Water on Mars could be used for dringking

B. There might be some kinds of life on Mars

C. NASA would send astronauts to journey to Mars

D. NASA confirms the best-ever evidence for water on Mars