1, the sum of even number and even number is still even number, and the sum of odd number and odd number is even number, so when taking it, even number is not limited, but odd number must have even number.

2, four numbers can be taken at will, but it is still a truth, the sum of odd numbers and even numbers is even numbers, and the sum of odd numbers and even numbers is odd numbers.

It is inconvenient not to write the calculation process here. Just a quick reminder.