The `Collections.unmodifiableList(list1)` method creates a read-only view of `list1`, meaning that any attempt to modify `list2` directly would result in an exception. However, modifications to `list1` are still reflected in the unmodifiable view `list2` because both lists point to the same underlying collection. Therefore, printing `list1` and `list2` will both output `[A, B, C]` since `list1` was modified by adding the element "C".