2. 外语
  3. The main reason we explore Mars is to determine if life ever existed on the planet. We have tried for centuries, starting with 【

The main reason we explore Mars is to determine if life ever existed on the planet. We have tried for centuries, starting with 【

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问题     The main reason we explore Mars is to determine if life ever existed on the planet. We have tried for centuries, starting with 【B1】______and lately with satellites, landers and rovers. We have 【B2】______ for it directly and indirectly. No luck so far. Some think life has never been there. Others think it was there in the past but is now gone. Many think why bother, but that’s a whole different story. I think we are 【B3】______in the wrong places. Here is why.
    The surface of Mars is 【B4】______cold and dry. Cosmic and solar 【B5】______reach the surface by the thin atmosphere, and the soil contains strong oxidants (氧化剂) that destroy organic 【B6】______. Fat chance for life. But it wasn’t always so.
    Early in its history Mars was warmer and 【B7】______enough for the development of rivers, lakes and perhaps oceans. The atmosphere was thicker and the protective magnetic (磁的) field was switched on. Mars might be 【B8】______today, but life would have been possible in the past. 【B9】______
    But first we need to find a promising location, and that means reconstructing Martian history. 【B10】______, what type of minerals formed and if the geochemical conditions were compatible with life. Once promising sites are identified, we need to find out if there are 【B11】______
【B2】
选项
答案searched
解析 语义推断题。分析句子结构可知，该句缺少谓语，故空格处应填入谓语动词。而空格前是have，句子使用现在完成时，空格处的动词要使用过去分词。由上句可知，人们使用望远镜、卫星、着陆器和漫游车进行探测，此句也讲探索方式，因此空格处单词应该具有“探索，探测”之意。结合录音可知，答案为searched。
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