US researchers have found traces of an ancient lake on Mars recently, increasing hopes of discovering evidence that billions of years ago the red planet hosted life.

The lake, which dates back some 3.4 billion years, appears to have covered as much as 80 square miles and was up to 1，500 feet deep, said the team from the University of Colorado.

“This is the first clear evidence of shorelines on the surface of Mars，” said Boulder's research associate, Gaetano Di Achille, in a study published in the latest edition of Geophysical Research Letters.

“The identification of the shorelines and accompanying geological evidence allows us to calculate the size and volume of the lake, which appears to have formed about 3.4 billion years ago.”

Analysis of the images has shown the water carved out the canyon(溪谷) in which it was found, which then opened out into a valley depositing(使淤积) sediment(沉积物) which formed a delta(三角洲)．

“Finding shorelines is a great discovery to us”， said assistant professor Brian Hynek, adding it showed the lake existed at a time when Mars was thought to have been cold and dry.

Scientists believe the oldest surfaces on Mars formed during the wet and warm era known as the Noachan epoch, about 4.1 billion to 3.7 billion years ago.

The newly discovered lake is believed to date from the Hesperian era and postdates the end of the warm and wet period on Mars by 300 million years, according to the study.

Scientists believe deltas next to the lake may well hold secrets about past life on Mars as such places on Earth have become the natural deposits of organic carbon and other markers of life.

16．The size of the lake found on Mars is ________．

A．80 square miles 

B．1，500 square miles

C．3.4 billion square miles 

D．300 million square miles

17．When the lake existed, the weather on Mars was ________．

A．hot and wet  B．wet and warm

C．cold and dry  D．cold and wet

18．Why do scientists think deltas near the lake may hold secrets about past life on Mars?

A．Because similar places on Earth have become natural deposits of markers of life.

B．Because someone has put secrets about past life on Mars there.

C．Because past life has been found in other deltas on Mars.

D．Because some people are said to have already seen life marks there.

19．Which of the following statements is NOT true according to the passage?

A．The Noachan epoch was a wet and warm era.

B．The lake might have existed 3.4 billion years.

C．The discovery can't fully prove that the Mars once hosted life.

D．The lake traces prove that there exists life on Mars now.

—Would she mind playing against her former teammates?

—________She is willing to play against any tough players.

A．I think so.  B．I'm not surprised.

C．Of course.  D．Not likely!

Eric didn't feel at ________ ease in the party，because he was afraid of losing ________ face.

A．the; a   B．an; /  C．/; the  D．/; /

—Have the peace talks broken down?

—Yes.Armed conflict is ________ to break out between the two countries.

A．likely  B．possibly

C．probably  D．gradually

I guess we've already talked about this before but I'll ask you again just________．

A．by nature  B．in return

C．in case  D．by chance

The results of the sports meeting will be ________ on Sunday morning.

A．put away  B．put off

C．put up  D．put down

Although the couple didn't choose to sleep in the wild instead of in the hotel, it________unexpectedly beautiful.

A．turned up  B．turned out

C．turned down  D．turned around

People in these countries demand equal treatment for all，________race, religion or sex.

A．in defence of  B．regardless of

C．instead of  D．in support of

Jane's always nervous when she has to make a speech; she must accustom herself to be ________ when she is with people.

A．at ease  B．in disguise

C．at risk  D．in relief

The kitchen is often the busiest room in a household, so it's important to make sure it ________well.

A．smoothes  B．functions

C．pays  D．measures