21．A　推理判断题。根据第四段…scientists have become increasingly confident they will find Martian life forms.Europe and America's robot explorers have found proof that water, mixed with soil, exists in large amounts on the planet.的内容，我们知道科学家越来越相信火星上存在生命，因为有证据表明火星土壤中存在大量的水，故可断定水是生命存在的关键要素。

　　22．B　推理判断题。根据倒数第二段…The gas is a waste product of living creatures and could be produced by microbes living in the red planet's soil.可知，火星大气层中存在甲烷的迹象，而甲烷是活着的动物产生的废物，据此科学家推断这可能是生活在火星上的微生物产生的。故可得出结论：火星上可能存在微生物，主要证据是在火星大气层中发现了甲烷的迹象。

　　Ⅲ.Time and tide wait

　　no man. My mother is becoming a

　　woman quietly. She

　　been busy running after us all the years. My father is very busy every day outside.

　　the heavy burden falls on my mother’s

　　. Because my school is far from my home, I have to go to school by the/　 train and my mother sees me off at the station every time. I often choose a seat

　　is close to the window, so I can see her.However, I always can’t help

　　tears from my eyes. All the buildings and people outside the window disappear. I wave

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