Let p, q, r and s be natural numbers such that
p - 2016 = q + 2017 = r - 2018 = s + 2019
Which one of the following is the largest natural number?

Correct Answer: (C) r

Setting each expression equal to a constant $k$: $p = k + 2016$, $q = k - 2017$, $r = k + 2018$, and $s = k - 2019$. Comparing these values reveals that $k + 2018$ is strictly greater than all other expressions, so $r$ is the largest natural number.