Mars has provoked much speculation on the possibilities _1_
of life beyond Earth than any planet in the Solar System. _2_
The presence of water is a prerequisite for the existing of life. _3_
Therefore, "follow the water" has been NASA' s chief guideline for the exploration of red planet. Although Mars experiences _4_
seasons like on Earth and has polar caps which composed of _5_
cold. But evidence is rapidly accumulation Mars was once much _6_
wetter, with amore clement climate. This evidence comes from orbiting satellites and from data collected by roving landers.
Since 1970s, space probes to Mars have revealed numerous _7_
Features apparent carved by flowing water, such as winding, branched valleys resembling dried-out streambeds and giant outflow channels gouged by catastrophic floods. Recent high-resolution imagery from the Mars Global Surveyor Mars Orbiter Camera and the Mars Odyssey THEMIS reveal numerous _8_
examples of branched valleys that form tightly-packed, integrated drainage systems. These channels origins at topographic high _9_
points; the valleys widen "downstream" some even displaying inner valleys. The valley networks exhibit morphometric characteristics, including network densities, comparative to these _10_
of terrestrial drainage basins. These features were most likely produced by rainfall, during wetter, warmer periods in the past.

答案：

1. much-more

2. any + other

3. existing-existence

4. a-the

5. 去掉which

6. Mars前加that

7. 1970s前加the

8. reveal- reveals

9. origins-originates

10. comparative-comparable