Why can append to a geometrically growing dynamic array be amortized O(1) even though one…

Why can append to a geometrically growing dynamic array be amortized O(1) even though one append may be O(n)?

1. Resizing never copies existing elements.
2. The total copying across n appends is O(n), so it spreads to O(1) per append.
3. Average-case and amortized analysis mean the same thing.
4. The array reserves infinite memory on its first append.