Suppose $P$ is a set containing n distinct elements. Let $S=\left\{\right(x,y,z)\mid x,y,z,\in ,P$ and at least two of $x,y,z$ are equal }.

The number of elements in $S$ is

• A

  $n(3n-2)$

• B

  $n^2(n-2)$

• C

  $n^3{-}^n{C}_3$

• D

  $n(5n-4)$