在maninus的提示下，研究了一下关于485 pending > 180 天，AC21和140的关系。找到
了这个： http://www.murthy.com/news/UDportme.html
2003年8月11号有一个memo:
“
Revocation or Withdrawal of the I-140 Petition
The Memo provides that the approved I-140 petition remains valid even if the
original sponsoring employer requests its revocation, as long as the I-485
application has been pending at least 180 days at the time of the revocation
or withdrawal. Those who chose concurrent filing enjoy an advantage, as
they are accruing time toward
