Which of the following is considered subnet ID $($SN$.$ ID$)$ for a sub$-$network with $\frac{?}{25}?$

a$.77\mathrm{.}99\mathrm{.}50\mathrm{.}64$

b$.77\mathrm{.}99\mathrm{.}50\mathrm{.}192$

C$.,77\mathrm{.}99\mathrm{.}50\mathrm{.}128$

d$.77\mathrm{.}99\mathrm{.}50\mathrm{.}32$

e$.$ None of the choices