Some people viewed the findings with caution, noting that a cause-and-effect relationship between passive smoking and cancer rem

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问题 Some people viewed the findings with caution, noting that a cause-and-effect relationship between passive smoking and cancer remained______.

选项 A、to be shown
B、to have been shown
C、to have shown
D、being shown

答案A

解析 非谓语动词。根据句中的意思可知是一般将来时态,所以应选择动词不定式的非谓语作宾语。故答案为A。
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