单选题 Some people viewed 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

【正确答案】 A

【答案解析】[解析] remain意为“依然；继续存在”，remain to do意为“仍然是……”，例如：Their object remains to investigate the matter thoroughly. 他们的目的仍然是彻底调查这一事件。remain to be done结构意为“某事有待去做”，例如：Many problems remain to be settled. 许多问题有待解决。由此可见D项错误。由于relationship和show是逻辑动宾关系，因此该不定式应该使用被动形式，所以B项错误。由于remain后的不定式是仍然未发出的动作，故不能使用完成形式，所以C项错误。