参考答案

正确答案：B
解析：本题为细节推断题。在第五段中提到“Perhaps the greatest puzzle of all is not why some people are left-handed, but rather why so few are.”(也许最让人迷惑不解的并不是为什么有些人是左撇子，而是为什么他们的人数这么少。)，“puzzle (迷)”即“not known”。