Scientists have found no of life on Mars so far,though great efforts have made on the rese

发布时间：2020-08-17 13:40:02

Scientists have found no     of life on Mars so far,though great efforts have made on the research.
A. symbols
B. signs
C. marks
D. signals

网友回答

A. symbols
(答案→)B. signs
C. marks
D. signals
解析：signs 迹象；symbols 象征；marks 标志；signals 信号。
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