US researchers have found traces of an ancient lake on Mars recently, increasing hopes of

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 acpanying 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) 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 bee the natural deposits of organic carbon and other markers of life.
【小题1】The size of the lake found on Mars is     .A．80 square miles B．1,500 square miles C．3.4 billion square milesD．300 million square miles【小题2】When the lake existed, the weather on Mars was     . A．hot and wet B．wet and warm C．cold and dryD．cold and wet【小题3】Why do scientists think deltas near the lake may hold secrets about past life on Mars?A．Because similar places on Earth have bee 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.【小题4】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.A