Mars is extremely cold even in summer,and the streaks are in places where the temperature is as low as minus 10 degrees Fahrenheit.But salt can lower the freezing point of water and melt ice.

　　The source (源头) of the water is a mystery.Scientists noted it could be melting ice.It could be an underground aquifer,which is rock or sand that can hold water.It is possibly water vapor from the thin Martian atmosphere,or it may be a combination.Michael Meyer,lead scientist for NASA’s Mars exploration program,said the only definitive way for now to determine whether there’s life on Mars is to collect rocks and soil for analysis on Earth—something a U.S.lander set for lift-off in 2020 will do.

　　1.What would be the best title for the text?

　　A.Streams of Water Spotted on Mars

　　B.Astronauts Will Land on Mars

　　C.NASA’s Mars Exploration Program

　　D.A Breakthrough in the Exploration of Mars

　　2.According to John Grunsfeld,there seems to be　 on Mars. 

　　A.salty waterB.standing water

　　C.rocket fuel D.human beings

　　3.Scientists are uncertain about the 　of the water on Mars. 

　　A.state B.source

　　C.temperature D.taste

　　4.What matters to the existence of liquid water on Mars?

　　A.The distance from the sun.

　　B.The favorable climate.

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