Close test. （每题2分，共12分）

There may be life on Mars(火星). We know1 about Mars than about any other planet （行星）. But astronomers are still guessing about many things.2 example, we think that on Mars 3 may be changes of weather during the year. Our own weather 4 from winter to summer. Perhaps it is the same on Mars. In Mars' mid-summer we can see brown places on the planet. In mid-winter these places are white.5 some scientists believe that plants grow on Mars during mid-summer and change color in winter. They do not 6 that there are green fields on Mars. But perhaps there is some kind of life.