請教：I-140要求補充材料

接到通知要求補充材料，如下：

1. Submit evidence to establish how to benefit of the self-petitioner's work is of national importance. What effect would the proposed employment of the individual alien have on the United States as a whole?
2. Submit evidence to persuasively establish that national interest would be adversely affected if the beneficiary were required to obtain labor certification from the U.S. Department of Labor. Would a U.S. worker with the same minimum qualifications be able to perform the same occupation and serve the national interest to a similar degree? How will the individual alien serve the national interest to a substantially greater degree that other individuals having similar credentials in the field? Please submit persuasive documentary evidence to substantiate your response.

在已提供的材料中，已有10封推薦信，是不是還要追加推薦信？如果是，多少封為宜？
還要補充哪些材料呢？有點兒不知道從何下手。請大家幫幫忙，萬分感謝！