Learning to write is learning to think. You don’t know things clearly you can write them

Learning to write is learning to think. You don’t know things clearly you can write them down.
A. unless
B. if
C. since
D. whether

(答案→)A. unlessB. ifC. sinceD. whether解析：unless 除非，如果不；if是否，如果；since由于，自从……以来；whether是否。句意：学习写作就是学习思考。如果你不能把它们写下来，你就不能了解事物。结合语境可知选A。

我明天再问问老师，叫他解释下这个问题