MathNet 2022-part-04 — 197 problems (EN–VI) Question 194

At most how many of the sums $x+y$, $x+z$, $x+w$, $y+z$, $y+w$ and $z+w$ can be odd, if $x$, $y$, $z$ and $w$ are natural numbers?

(A) 2
(B) 3
(C) 4
(D) 5
(E) 6