One of the most important issue they had to consider in the

One of the most important issue they had to consider in the UN climate conference in Copenhagen was__that__ rich-poor cooperation on climate change.
主语是One of the most important issue
谓语是was
宾语是that,that的具体内容是 rich-poor cooperation on climate change.
they had to consider in the UN climate conference in Copenhagen 修饰的是主语issue
rich-poor cooperation on climate change是贫富国家之间关于气候变化的合作.