回複：Xiaobaitu, Please.

1. When I leave U.S., should I turn in both bottom parts (left and right) or just the right part?
A: Right one only.
2. When I leave U.S., does any authority stamp my passport to indicate I leave U.S.?
I remembered when I l left China years ago, at Beijing airport I was stamped on my passport.
A: No. You will not going through US immigration check. You will be checked only when you enter US.