以下这道题``选哪个?We must make some investigations we can draw any conclusion.
问题描述：
以下这道题``选哪个?We must make some investigations we can draw any conclusion.
We must make some investigations we can draw any conclusion.
A.since
B.before
C.until
D.when
答
选before
意思为在我们可以得到任何结论之前必须作出一些研究.