Question from GMAT Prep S/w

Is the product of certain pair of integers even?

a. The sum of the integers is odd.
b. One of the integers is even and the other is odd.

OK, now the answer given is D, both the statements fulfill the requirements.

I have a problem understanding statement "a". It says the sum of the integers is Odd. what if one of the integers is Zero, then how does that fulfill "a".