you don't say so是什么意思

问题描述:

you don't say so是什么意思
题目是这样的"To tell you the truth,I became a college student at 15."
“——————————”
A.You myst beB.Thank goodnessC.You don't say so D.It doesn't matter
我觉得要选C但我不知道它具体是什么意

你不是这样说的吧