Show that there are $C(n + r − q_{1} − q_{2} −\dots − q_{r} −1, n − q_{1} − q_{2} −\dots − q_{r})$ different unordered selections of $n$ objects of $r$ different types that include at least $q_{1}$ objects of type one, $q_{2}$ objects of type two $,\dots, $ and $q_{r}$ objects of type $r.$
