阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。
A
There are no signs of little green men on Mars. But new discoveries offer a bit more hope that some form of life existed there in the past --- and perhaps is still there in the present. Methane gas(甲烷) and water have been found on the Red Plane. The presence of both suggests at least the possibility of life.
According to a new report in the journal, Science, the Mars rover, Curiosity, has detected spikes of methane in the Martian atmosphere. This gas is also found in the Earth’s atmosphere, and comes from animal and plant life, as well as from the environment itself. If there’s methane in Mar’s atmosphere, where is it coming from? Scientists aren’t sure. But it marks a big change. In September 2013, Curiosity found almost no traces of methane in the Martian air. Just weeks later, however, the rover picked up a whiff of(一点点) the gas.
The scientists don’t know whether the methane spikes are caused by some form of biological matter or by the geology of the planet. Christopher Chyba, a professor of astrophysics and international affairs at Princeton, says it’s best not to be too hopeful about biology on the Red Planet. “Hopes for biology on Mars have had a way of disappearing once Martian chemistry has been better understood,” he says. “But figuring out what’s responsible for the methane is clearly a key astrobiological objective --- whatever the answer turns out to be.”
The discovery of water on Mars is nothing new. For decades, scientists have had evidence that it flowed across the surface of the planet billions of years ago. But according to another new report in Science, while the surface water on Mars seems to be long gone, there’s a lot more of it left than most of people realize.
This report is also based on findings from Curiosity. Paul Mahaffy, of NASA’s Goddard Space Flight Center in Maryland, led the study. He says there is enough water on Mars “to cover the surface to a depth of about 165 feet.”
It is not easy to reach this water. Most of it is locked up in ice at the planet’s poles.
Why do scientists think there might be life on Mars?

A．Because the Mars rover has detected water on the planet.

B．Because there is evidence that little green men exist on the planet.

C．Because the Mars rover has found some plants on the planet.

D．Because both methane and water have been found on the planet.

What is the attitude of professor Christopher Chyba towards life on Mars?

A．Optimistic	B．Negative
C．Neutral	D．Indifferent

The water on Mars _______________.

A．still flows on its surface

B．covers the whole planet

C．is locked up in ice at the planet’s poles

D．only existed on it billions of years ago

In which column of a website can we read this text?

A．Culture	B．Entertainment
C．Science	D．Education

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