There are three boxes, one containing two red balls, one containing two white balls, and one containing a red ball and a white ball. at present

certificate

Take out a label from the box with a red ball and a white ball on it:

First, if one of the boxes is a white ball:

1. Because there can't be one white and one red in the box marked with one white and one red, there must be two white balls in this box;

2. Because there can't be two red balls in the box marked with two red balls, it is filled with one white and one red;

Because there are only two red balls left in the box marked with two white balls. Meet the requirements of this problem.

Second, if one is a red ball:

1. Because there can't be one white and one red in the box marked with one white and one red, there must be two red balls in this box;

2. Because there can't be two white balls in the box marked with two white balls, it is filled with one white and one red;

Because there are only two white balls left in the box marked with two red balls. Meet the requirements of this problem.