There seems to be a printing mistake here
If there are $(2n-1)$ terms instead of $(2n + 1)$ terms then $n^{th}$ terms of the A.P., G.P. and H.P. are the A.M., G.M. & H.M of the first and the last terms.
So, $a\ge b\ge c\, \&\, ac-b^{2}\left(B, D\right)$
otherwise if there are $(2n + 1)$ terms then the $n^{th}$ terms should be in decreasing order of $A.P., G.P$. & $H.P.$
i. e.$a\ge b\ge c \left(B\right)$