题目内容
20．It isimpossible（possible） for humans to live on Mars at present．分析 翻译：目前人类居住在火星上是不可能．
解答 答案：impossible．possible可能的，目前人类住在火星上是不可能的，故该用possible的反义词，是在possible前面加否定的前缀im，故答案为impossible．
点评 本题考查的是完成句子，答题时要根据上下文的语境和句意去答题．
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