After setting up a dual$-$boot installation with Windows $8\mathrm{.}1$ and Windows $10,$ how do you boot the system into Windows $8\mathrm{.}1?$

a$.$ Go into BIOS$/$UEFI setup and set the boot priority order to start with Windows $8\mathrm{.}1.$

b$.$ Start the system as normal; the oldest OS automatically loads.

c$.$ Start the system as normal; the newest OS automatically loads.

d$.$ Start the system and select the OS in the boot loader menu.