I-864问题：配偶申请绿卡，家庭收入主要来自被担保方的收入。 bypassus2013-07-22 22:19:16

I-864有这么个要求：
Evidence that his or her income will continue from the current source after obtaining lawful permanent resident status must be provided

请问出具什么材料可以满足这个要求？