请教NO2阅读中的一个句子

chuanweizuoUID??2189837

句子如下：
When the object is optimal resource allocation, that combination of legal methods should be used that most nearly yields the allocation that would exist if there were no external costs resulting from allocating resources through market activity.

后面那部分有三个that，主谓宾结构是什么？

wilyUID??2133996

主句that combination of legal methods should be used that most nearly yields the allocation
把第二个that 看成 the 就OK了
that combination of legal methods should be used为主语从句做主语
谓语YIELDS

[ 本帖最后由 wily 于 2006-8-21 23:54 编辑 ]