-Either one of these is OK: Dept. Chair, Dean, Vice President, president.
2.信上說“...the letter must also indicate whether the term and conditions of your emplolyment-based visa petition(or labor certification) continue to exist."
對於EB1A,是不是隻要證明自己繼續從事同一領域就可以了?
-Not enough. For all EB I-485 (EB1A/B, EB2, etc.), you need to indicate your position is permanent (you do not need to use "Permanent" this word), but use this kind of sentence: "Dr. XXX's current psosition has an unlimited duration, and thus Dr. XXX will ordinarily have an expectation of continued employment unless there is good cause for termination.”
So, you may add this sentence I suggest here to your daft of the letter.