这是人类进化中最大的问题之一，它已经困扰了科学家数十年之久。
The question, one of the biggest in human evolution, has plagued scientists for decades.
我们把这类人称为联觉者，自从联觉现象被人类所认识以来，它已经困扰了人脑科学家们长达一个多世纪之久。
Such people are known as synaesthetes, and the phenomenon of synaesthesia has puzzled brain scientists since it was recognised over a century ago.
我不知道为什么我没有更早地想到它，因为这个问题已经困扰了我几个月了，如果不是几年的话！
I don't know why I didn't think of it sooner, because this problem has been bugging me for months, if not years!
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