When ZnS and PbS minearls are present together, then NaCN is added to separate them in the froth floatation process as a depressant, because :
A. `Pb(CN)_(2)` is percipitated while there is no effect on ZnS
B. ZnS forms soluble complex,`Na_(2)[Zn(CN)_(4)]`
C. PbS forms soluble complex,`Na_(2)[Pb(CN)_(4)]`
D. both (1) and (2)