# $l,m,n$ are the $p^{th},q^{th}$ and $r^{th}$ terms of a GP and all positive then $\begin{vmatrix}\log l&p&1\\\log m&q&1\\\log n&r&1\end{vmatrix}$ equals
$(a)\;3\qquad(b)\;2\qquad(c)\;1\qquad(d)\;zero$