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Even x Even = Even
Even x Odd = Even
Odd x Odd = Odd
With that in mind...
xz is even. This tells us that x and z are both even or one is even, and the other is odd.
From the question, we know that x and y are factors of z, and as such, the lowest value for z is xy. Replacing z with xy, we find that unless both x and y are odd, xy (thus z) must be even. Because statement 1 tells us that xz is even, x and y (the factors of z) can't both be odd. Going back to Even x Odd = Even, xy must be even. As a result, z must be even. Sufficient.
Y is even. Going back to the rules above, we know that anything multiplied by an even number is even. Since y is a factor of z, it follows that z must be even. Sufficient.
Since both are sufficient on their own, I take answer D.
1) Since x is a factor of z. All the factors of an odd number are always odd. Since x is a factor of z and if z is odd x has to be odd but
that can not be true because that will make 'xz' odd. So they are both even. SUFFICIENT.
2) Odd numbers can not have even factors. So, z is even.