Given positive integer $r>1,n>2$ and the coefficient of $(3r{)}^{\mathrm{th}}$ and $(r+2{)}^{\mathrm{th}}$ terms in the binomial expansion of $(1+x{)}^{2n}$ are equal. Then

• A

  $n=2r$

• B

  $n=3r$

• C

  $n=2r+1$

• D

  none of these