On the one hand, the robots sent to the planets have not yet found any 24. of li

On the one hand, the robots sent to the planets have not yet found any 24.________ (迹象) of life on Mars, but they have found evidence that water 25.________ freely over the planet's surface millions of years ago. 26.________ addition, water in the form of ice exists below some 27.p________ of the Martian surface today.

On the other hand, 28.d________ life on Mars would change the present view of the Universe and also give a big push toward man's work there. But a group of experts 29.o________ by President Barack Obama told him last October that US 30.________ (太空) policy should now focus on sending human beings to Mars instead of 31.________ (又一，再一) moon landing. Michael Griffin, a former head of NASA, believes 32.________ a human trip to Mars could be 33.p________ by 2037.

试题答案

24.signs　25.flowed　26.In　27.parts　28.discovering

29．organized　30.space　31.another　32.that　33.possible