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    34．Although there is no life on Mars now, some scientists think that there some form of life a long time ago . A．must be B．may have been C．can have been D．could be 【查看更多】

     

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    Although there is no life on Mars now , some scientists think that there        some form of life a long time ago .

           A．must be    B．may have been C．can have  been      D．could be

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