Number of BTs with Unlabelled nodes is (2n C n )/(n+1)
Number of BTs with labelled nodes is (2n C n ) * (n!) /(n+1) .
So, answer is option C.
If question have asked about BTs with labelled nodes then answer is B i.e picking n out of 2n people i.e 2n C n then n can be arranged in n! ways