$p, q, r$ are three unequal numbers in AP. If $q-p$, $r-q$ and $p$ are in GP, the $p\;:\;q\;:\;r$ equals

Question

$(a)\;1:3:4\qquad(b)\;1:2:3\qquad(c)\;2:3:5\qquad(d)\;1:2:4$