Reciprocal value of  expression  $\frac{{\displaystyle \underset{0}{\overset{n}{\int }}\left(\text{Fractional part of }x\right)}dx}{{\displaystyle \underset{0}{\overset{n}{\int }}\left(\text{Integral part of }x\right)}dx}=$

• A

  $\frac{n\left(n-1\right)}{2}$

• B

  $\frac{2}{n\left(n-1\right)}$

• C

  $n-1$

• D

  $\frac{1}{n-1}$