1.And so, we've come to cash this check, a check that will give us upon demand the riches of freedom and the security of justice.
问题1: upon是介词，demand只能是名词了，那么the riches of freedom and the security of justice可以分析为demand的限制性同位语吗？
2.We hold these truths to be self-evident, that all men are created equal.
3.The marvelous new militancy which has engulfed the Negro community must not lead us to a distrust of all white people, for many of our white brothers, as evidenced by their presence here today, have come to realize that their destiny is tied up with our destiny.
问题3：as evidenced by their presence here today这里的as是关系代词指代white people吗，补全省略成分是否为as (are) by their presence here today？
1 the riches of freedom and the security of justice 为gives的直接宾语，on demand是时间状语。直接宾语后移到句末予以强调，这叫做宾语后移。
2 你没有看完整的句子。完整的句子是这样的：We hold these truths to be self-evident, that all men are created equal, that they are endowed by the Creator with certain unalienable rights, that among these are life, liberty, and the pursuit of happiness. 三个that从句是these truths的同位语，并不是形容词的补足语。
3 as evidenced by their presence here today = as is evidenced by their presence here today，是传统语法的非限制性定语从句，as指代的是整个句子的内容，而不是white people。这个as从句可以置于句首、句末或句中位置。