哪个对哪个错

在看OG10-161时，随手写了如下几种表达方式，请NN帮忙看看有几个是正确的

1/ the wolf density
2/the population density of wolf
3/the wolf’s population density
4/the wolf population’s density
5/the density of wolf’s population
6/the density of wolf population

写完我也有点晕了