1) should address if your study is based on the need of USA, not just based on your own interest, that is why USA needs such study.
2): equivalent to two questions, 1) if effect of your work/study is in national scope, 2)what are effects/influences of your work on national interest etc?
It seems that your original petition letter did not well address the three prongs of NIW.
You need to talk to your lawyer about your RFE. You would fail your RFE if you answered your RFE based on your such understanding.
Just for your reference
yjy_wang@yahoo.com