number properties

[sud21]

If a+b=c+d, where a, b, c, and d are integers. How many of them could be even?

[Anurag@Gurome]

If a+b=c+d, where a, b, c, and d are integers. How many of them could be even?

If the sum is even, then both the integers of either pair must be either odd or even.
If the sum is odd, then one of the integers of either pair must be even and other one must be odd.

Hence, either none of them or two of them or all of them could be even.