So far no life has been found outside the earth but while some scientists are actively se

问题补充：

So far no life has been found outside the earth, but while some scientists are actively searching for living things in outer space, others firmly believe there .

A. mustn’t be

B. may not be

C. can’t be

D. won’t be

答案：

A. mustn’t be

B. may not be

(答案→)C. can’t be

D. won’t be

解析：考查情态动词。mustn’t不表示否定推测，may not“可能不”，可能性没有can’t大；won’t“不会”，不表示推测。根据firmly可知，其他人坚信不可能存在外太空生物。故选C。