The man is so stubborn that ________ he makes up his mind, nothing can be done to change it．

The man is so stubborn that ________ he makes up his mind, nothing can be done to change it．

A.after

B.when

C.before

D.once

答案及解析： D

从后半句来看，条件和时间意味十分强烈，只有once才能表达。