A man does not know the difficulty of anything he does it personally.
A. although
B. if
C. because
D. unless
网友回答
A. although
B. if
C. because
(答案→)D. unless
解析:A. although尽管,引导让步状语从句,一般置于句首,用逗号隔开;B. if假如,尽管,是否C. because 因为,引导原因状语从句;D. unless除非,否则;句意:一个人不可能知道所有事情的难度,除非他亲自动手做它。故选D.