——You are so lucky.——What do you mean______saying that?

题目

——You are so lucky.——What do you mean______saying that?
—You are so lucky.
—What do you mean______ that?
A.for
B.in
C.of
D.by
说下原因,

答案

D
By的意思是通过,意思为通过说那个,应该算一种固定搭配了吧,在美剧里经常听到.