以下代码执行后，数组 arr 的内容是（ ）

1 int arr[6] = {1, 2, 3, 4, 5, 6};2 for (int i = 0; i < 6; i += 2) {3   arr[i] = arr[i] + arr[i+1];4   arr[i+1] = arr[i] - arr[i+1];5   arr[i] = arr[i] - arr[i+1];6 }