Some people viewed the findings with caution,noting that a cause-and-effect relationship between passive smoking and cancer remains ___________.一碰到这种题目我就不知道思路在哪?

Some people viewed the findings with caution,noting that a cause-and-effect relationship between passive smoking and cancer remains ___________.一碰到这种题目我就不知道思路在哪?
Some people viewed the findings with caution,noting that a cause-and-effect relationship between passive smoking and cancer remains ___________.
一碰到这种题目我就不知道思路在哪?

Some people viewed the findings with caution,noting that a cause-and-effect relationship between passive smoking and cancer remains ___________.一碰到这种题目我就不知道思路在哪?
A. 因为吸二手烟和癌症之间的因果联系还没有显示出来,所以是to be shown,
b选项都已经证实了,何必还要不定式to了?不选C的原因和不选b一样,

A
吸二手烟和癌症的因果关系有待揭示。

remain to be done 有待。。。