863211老师和皮匠老师，我在2006年初由公司A(a big company)递交了Perm并获得批准，随后I-140在2007获得批准, 在2007年7月递交I-485。2009年初裁员, 2009年5月到公司B(a mid-size company)工作，于同月收到USCIS的RFE (Employment Letter)并由公司B回复(no response from USCIS)。后在2009年9月换到公司C(a small company)。现在又有一机会到公司D (a start-up company)。我的问题是：
(1)Is this a problem to change company so often (change jobs less than half year again)? (2) My current salary is lower than that in A (however, higher than the prevailing wage when I applied Perm), is it fine? (3) How USCIS judge my field is similar to that in Perm or not, just from the employment letter? (4)I can ask my manager write a letter, which can match the content in Perm but is different from daily job, how USCIS know that? (5) I often heard the status of “Pre-Adjusted” or “Pre-approved”I-485, what does it mean and how can I know whether my 485 is pre-approved or not? (6) If my 485 is pre-approved, will USCIS ask RFE again? (7) The current company is small (C or D just has a few employees). Is the size of an company an issue?
Thank you for your answer.