1 .
Let $n \geq 2$ be an integer and let $S$ be a set of $m$ integers. What is the minimum value
of $m$ such that we can guarantee that $S$ contains at least two elements whose difference
is divisible by $n$?
(a)
$n - 1$
(b)
$n + 2$
(c)
$n + 1$
(d)
$n$