翻译：存在未被标记的零元素并且其所在行列中未被标记的零元素均至少有两个可得到最优解。此时从剩余零元素最少的行或列开始选零元素画圈然后划掉同行同列的其它零元素反复进行直到所有零元素均被圈出或划掉为止。

If there are unmarked zero elements, and there are at least two unmarked zero elements in the rows and columns they belong to, the optimal solution can be obtained. At this point, starting from the row or column with the fewest remaining zero elements, select zero elements to be circled, and then cross out other zero elements in the same row or column. Repeat this process until all zero elements are circled or crossed out.