A.must be B.may have been C.can have been D.could be ,为什么呢,

A.must be B.may have been C.can have been D.could be ,为什么呢,
Although there is no life on Mars now,some scientists think that there______some form of life a long time ago.

斑点狗1985 1年前已收到3个回答举报

zhuyongyuan 幼苗

共回答了13个问题采纳率：92.3% 举报

表示曾经有过,所以是Have been
表示猜测,所以是may

1年前

你的致命伤幼苗

共回答了137个问题举报

Although there is no life on Mars now, some scientists think that there_may have been some form of life a long time ago过去完成时延续性动作，强调对现在有影响

1年前

银铃1987 幼苗

共回答了9个问题举报

may 在此处表示一种猜想而不是“将要”，整个意思是：也许有过生命，故选b

1年前

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