http://www.greencardforphd.com/downloads/GreencardforPhd_ebook.
在网上又找到了上面这个pdf文件，里面写到
ETA-750b: This form is used for employment certification and is generally
filled by employer. In the case of self-petitioning, this form is usually
not necessary but is optionally filled by some applicants.
这样看起来好像说，如果我自己petition就可以不用填这个表格。
