e-filing 问题--谢谢

有几个关于I140 E-FILING的初级问题,可能听起来有些幼稚. 提前谢谢大家的回答.
1. USCIS 网页(http://149.101.23.2/graphics/formsfee/forms/e-i-140.htm#purpose)提到"This form is filed on behalf of an alien, and not by the alien." 什么意思?不是说我们自己不能E-FILE,只能请律师吧?

2. E-FILING 的过程是不是:
a. I140 form and the fee by e-filing;
b. At the end of e-filing, obtain a confirmation receipt number.
c. Mail the cover letter and supporting materials (papers, awards,
etc.) with the receipt number.

3. Filing question2: Are you authorized for Centralized Filing? 这个怎样判断?一般情况是NO吗?

谢谢