if an $802\mathrm{.}11$n client tries to use an $802\mathrm{.}11$ac access point, $\_\_\_\_\_\_\_\_.$

they will not be able to communicate

they will communicate using $802\mathrm{.}11$n

they will communicate using $802\mathrm{.}11$ac

either they will communicate using $802\mathrm{.}11$n or they will communicate using $802\mathrm{.}11$ac