Nobody knows the age of the earth _____ certain.

题目

Nobody knows the age of the earth _____ certain.
A.by
B.in
C.with
D.for
是固定搭配?看到certain就选for certain

答案

是的,for certain 一般和know 的否定式连用：
not know...for certain 不确切知道:
for certain 无疑地； 确定地
I don’t know for certain how many people are coming.
=I don’t know how many people are coming for certain
我不确定到底有多少人会来.
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