$7.$ Of the six points $($u$,$ v$,$ w$,$ x$,$ y and z$)$ in Figure $1,$ feasible production points in this economy include a$.$ only points u$,$ v$,$ w$,$ x and y

b$.$ only points u$,$ x$,$ and y

c$.$ only points u$,$ x$,$ y and z

d$.$ only point z