Given triangle $ABC$, let $D$ be an inner point of the side $BC$. Let $P$ and $Q$ be distinct inner points of the segment $AD$. Let $K=BP\cap AC$, $L=CP\cap AB$, $E=BQ\cap AC$, $F=CQ\cap AB$. Given that $KL\parallel EF$, find all possible values of the ratio $BD:DC$.