A router configuration includes the following: Router$($config$)$#int fa$0/0$

Router$($config$-$if$)$#ip address $172\mathrm{.}16\mathrm{.}1\mathrm{.}0255\mathrm{.}255\mathrm{.}255\mathrm{.}0$ Router$($config$)$#int fa$0/1$

Router$($config$-$if$)$#ip address $172\mathrm{.}16\mathrm{.}2\mathrm{.}0255\mathrm{.}255\mathrm{.}255\mathrm{.}0$ Router$($config$)$#int s$0/0$

Router$($config$-$if$)$#ip address $172\mathrm{.}16\mathrm{.}3\mathrm{.}0255\mathrm{.}255\mathrm{.}255\mathrm{.}0$

The router is running RIP v$1.$ Would it be sensible to configure serial $0/1$ with the IP address $172\mathrm{.}16\mathrm{.}20\mathrm{.}0255\mathrm{.}255\mathrm{.}255\mathrm{.}252?$

a$)$ No$,$ because this is not a valid subnet mask for a serial interface. No$,$ because this would create an overlap of IP addresses.

b$)$ No$,$ because the $172\mathrm{.}16\mathrm{.}4\mathrm{.}0$ address should be used next for consistency.

c$)$ No$,$ because this would involve VLSM which is not supported by RIP v$1.$

d$)$ Yes, this would be acceptable because it is on a different classful network.