If [x] denotes the greatest integer less than or equal to x then $\underset{n\to \infty }{Lim}\frac{\left[x\right]+\left[2x\right]+\mathrm{.....}+\left[nx\right]}{n^2}=$

• A

  x/2

• B

  x/3

• C

  x

• D

  0