Some people view the findings with caution noting that a cause－and－effect relationship be
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Some people view the findings with caution, noting that a cause-and-effect relationship between passive smoking and cancer remains______.
A．to be shown
B．to have shown
C．to have been shown
D．being shown
请帮忙给出正确答案和分析，谢谢！
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正确答案：A
remaintobeshown“尚待揭示”，不定式的一般式表示要实现的情况，其完成式表示已发生的情况。remaindoing“保持……；一直……”，如：Heremainedstandingforonehour．他一直站了一个小时。