朋友雖然在過去的5年中沒有在中國居住連續超過6個月，但是過去5年裏在美國總共居住的時間有限，可能不足30個月。
-Then, he probably is not qualified for N-400 yet until he meets the requirement of continuous residency (30 momths in the last 5 years).
另外，他在美國居住的日子，移民局那裏有精確的記錄可查嗎？
-I think USCIS system should have the record, but he may not be allowed to check it. He should have recorded his travel by himself.
因為離境除了航班記錄，護照上似乎沒有離境記錄，他中美往返多了以後自己都搞不清楚究竟每年在美國境內居住了多長時間？
