以下代码执行后，数组 arr 的内容是多少。

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

{{ select(1) }}

• {2,1,4,3,6,5}
• {1,2,3,4,5,6}
• {3,1,4,2,5,3}
• {1,3,2,5,4,6}